can, tty: elmcan CAN/ldisc driver for ELM327 based OBD-II adapters

Documentation/networking/device_drivers/can/elmcan.rst line 95

Quoted 9 lines · Max Staudt

Documentation/networking/device_drivers/can/elmcan.rst new file +9 -0

+    sudo ldattach \
+           --debug \
+           --speed 38400 \
+           --eightbits \
+           --noparity \
+           --onestopbit \
+           --iflag -ICRNL,INLCR,-IXOFF \
+           29 \
+           /dev/ttyUSB0  

I think you mean "30" here, not "29", right?

This is the elmcan driver. It does a surprisingly good job at turning ELM327 based OBD-II interfaces into cheap CAN interfaces for simple homebrew projects.

Please see the included documentation for details and limitations:
Documentation/networking/device_drivers/can/elmcan.rst

CC TTY maintainers for their opinion as this patch adds a new ldisc, taking the very last ldisc number available (29) without increasing NR_LDISCS (beyond the current 30).

Cc linux-can <[email protected]>

Cc Greg Kroah-Hartman <[email protected]>

Cc Jiri Slaby <[email protected]>

Signed-off-by Max Staudt <[email protected]>

---
Changes in v3:
- Now depends on c2faf737abfb for new ldisc number 30:

     https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git/commit/?h=tty-next&id=c2faf737abfb10f88f2d2612d573e9edc3c42c37

- Eliminated hardcoded string lengths (GCC will work its magic).
- Emit generic error frames if an error message couldn't be parsed.
- Silence driver startup and init (but still announce ldattach).
- Cleaned up comments, strings, readme.
- Removed sole module option "accept_flaky_uart".
I likely had EMI in earlier testing, which is gone now. This means we can stay strict, unless anyone objects.

Changes in v2:
- Moved to SocketCAN's rx-offload wrapper for NAPI, thus avoiding packets being reordered.
- Updated TTY ldisc code for Linux v5.17-rc3. A lot of cleanup has happened there lately.
- netif_stop_queue() is called earlier in _netdev_close().
- Minor cleanup: More helpful strings and return values.

---
 .../networking/device_drivers/can/elmcan.rst  |  325 +++++
 .../networking/device_drivers/can/index.rst   |    1 +
 MAINTAINERS                                   |    7 +
 drivers/net/can/Kconfig                       |   17 +
 drivers/net/can/Makefile                      |    1 +
 drivers/net/can/elmcan.c                      | 1250 +++++++++++++++++
 include/uapi/linux/tty.h                      |    3 +-
 7 files changed, 1603 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/networking/device_drivers/can/elmcan.rst
 create mode 100644 drivers/net/can/elmcan.c

Documentation/networking/device_drivers/can/elmcan.rst new file +325 -0

new file mode 100644
index 000000000000..7656d62dd58e
@@ -0,0 +1,325 @@
+.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause)
+
+ELM327 driver for Linux SocketCAN
+==================================
+
+Authors
+--------
+
+Max Staudt <[email protected]>
+
+
+
+Motivation
+-----------
+
+This driver aims to lower the initial cost for hackers interested in
+working with CAN buses.
+
+CAN adapters are expensive, few, and far between.
+ELM327 interfaces are cheap and plentiful.
+Let's use ELM327s as CAN adapters.
+
+
+
+Introduction
+-------------
+
+This driver is an effort to turn abundant ELM327 based OBD interfaces
+into full fledged (as far as possible) CAN interfaces.
+
+Since the ELM327 was never meant to be a stand alone CAN controller,
+the driver has to switch between its modes as quickly as possible in
+order to fake full-duplex operation.
+
+As such, elmcan is a best effort driver. However, this is more than
+enough to implement simple request-response protocols (such as OBD II),
+and to monitor broadcast messages on a bus (such as in a vehicle).
+
+Most ELM327s come as nondescript serial devices, attached via USB or
+Bluetooth. The driver cannot recognize them by itself, and as such it
+is up to the user to attach it in form of a TTY line discipline
+(similar to PPP, SLIP, slcan, ...).
+
+This driver is meant for ELM327 versions 1.4b and up, see below for
+known limitations in older controllers and clones.
+
+
+
+Data sheet
+-----------
+
+The official data sheets can be found at ELM electronics' home page:
+
+  https://www.elmelectronics.com/
+
+
+
+How to check the controller version
+------------------------------------
+
+Use a terminal program to attach to the controller.
+The default settings are 38400 baud/s, 8 data bits, no parity, 1 stopbit.
+
+After issuing the "``AT WS``" command, the controller will respond with
+its version::
+
+    >AT WS
+
+
+    ELM327 v1.4b
+
+    >
+
+Note that clones may claim to be any version they like.
+It is not indicative of their actual feature set.
+
+
+
+How to attach the line discipline
+----------------------------------
+
+Every ELM327 chip is factory programmed to operate at a serial setting
+of 38400 baud/s, 8 data bits, no parity, 1 stopbit.
+
+The line discipline can be attached on a command prompt as follows::
+
+    sudo ldattach \
+           --debug \
+           --speed 38400 \
+           --eightbits \
+           --noparity \
+           --onestopbit \
+           --iflag -ICRNL,INLCR,-IXOFF \
+           29 \
+           /dev/ttyUSB0
+
+To change the ELM327's serial settings, please refer to its data
+sheet. This needs to be done before attaching the line discipline.
+
+Once the ldisc is attached, the CAN interface starts out unconfigured.
+Set the speed before starting it:
+
+    # The interface needs to be down to change parameters
+    sudo ip link set can0 down
+    sudo ip link set can0 type can bitrate 500000
+    sudo ip link set can0 up
+
+500000 bit/s is a common rate for OBD-II diagnostics.
+If you're connecting straight to a car's OBD port, this is the speed
+that most cars (but not all!) expect.
+
+After this, you can set out as usual with candump, cansniffer, etc.
+
+
+
+Known limitations of the controller
+------------------------------------
+
+- Clone devices ("v1.5" and others)
+
+  Sending RTR frames is not supported and will be dropped silently.
+
+  Receiving RTR with DLC 8 will appear to be a regular frame with
+  the last received frame's DLC and payload.
+
+  "``AT CSM``" not supported, thus no ACK-ing frames while listening:
+  "``AT MA``" will always be silent. However, immediately after
+  sending a frame, the ELM327 will be in "receive reply" mode, in
+  which it *does* ACK any received frames. Once the bus goes silent
+  or an error occurs (such as BUFFER FULL), the ELM327 will end reply
+  reception mode on its own and elmcan will fall back to "``AT MA``"
+  in order to keep monitoring the bus.
+
+
+- All versions
+
+  No full duplex operation is supported. The driver will switch
+  between input/output mode as quickly as possible.
+
+  The length of outgoing RTR frames cannot be set. In fact, some
+  clones (tested with one identifying as "``v1.5``") are unable to
+  send RTR frames at all.
+
+  We don't have a way to get real-time notifications on CAN errors.
+  While there is a command (``AT CS``) to retrieve some basic stats,
+  we don't poll it as it would force us to interrupt reception mode.
+
+
+- Versions prior to 1.4b
+
+  These versions do not send CAN ACKs when in monitoring mode (AT MA).
+  However, they do send ACKs while waiting for a reply immediately
+  after sending a frame. The driver maximizes this time to make the
+  controller as useful as possible.
+
+  Starting with version 1.4b, the ELM327 supports the "``AT CSM``"
+  command, and the "listen-only" CAN option will take effect.
+
+
+- Versions prior to 1.4
+
+  These chips do not support the "``AT PB``" command, and thus cannot
+  change bitrate or SFF/EFF mode on-the-fly. This will have to be
+  programmed by the user before attaching the line discipline. See the
+  data sheet for details.
+
+
+- Versions prior to 1.3
+
+  These chips cannot be used at all with elmcan. They do not support
+  the "``AT D1``" command, which is necessary to avoid parsing conflicts
+  on incoming data, as well as distinction of RTR frame lengths.
+
+  Specifically, this allows for easy distinction of SFF and EFF
+  frames, and to check whether frames are complete. While it is possible
+  to deduce the type and length from the length of the line the ELM327
+  sends us, this method fails when the ELM327's UART output buffer
+  overruns. It may abort sending in the middle of the line, which will
+  then be mistaken for something else.
+
+
+
+Known limitations of the driver
+--------------------------------
+
+- No 8/7 timing.
+
+  ELM327 can only set CAN bitrates that are of the form 500000/n, where
+  n is an integer divisor.
+  However there is an exception: With a separate flag, it may set the
+  speed to be 8/7 of the speed indicated by the divisor.
+  This mode is not currently implemented.
+
+- No evaluation of command responses.
+
+  The ELM327 will reply with OK when a command is understood, and with ?
+  when it is not. The driver does not currently check this, and simply
+  assumes that the chip understands every command.
+  The driver is built such that functionality degrades gracefully
+  nevertheless. See the section on known limitations of the controller.
+
+- No use of hardware CAN ID filtering
+
+  An ELM327's UART sending buffer will easily overflow on heavy CAN bus
+  load, resulting in the "``BUFFER FULL``" message. Using the hardware
+  filters available through "``AT CF xxx``" and "``AT CM xxx``" would be
+  helpful here, however SocketCAN does not currently provide a facility
+  to make use of such hardware features.
+
+
+
+Communication example
+----------------------
+
+This is a short and incomplete introduction on how to talk to an ELM327.
+
+
+The ELM327 has two modes:
+
+- Command mode
+- Reception mode
+
+In command mode, it expects one command per line, terminated by CR.
+By default, the prompt is a "``>``", after which a command can be
+entered::
+
+    >ATE1
+    OK
+    >
+
+The init script in the driver switches off several configuration options
+that are only meaningful in the original OBD scenario the chip is meant
+for, and are actually a hindrance for elmcan.
+
+
+When a command is not recognized, such as by an older version of the
+ELM327, a question mark is printed as a response instead of OK::
+
+    >ATUNKNOWN
+    ?
+    >
+
+At present, elmcan does not evaluate this response and silently assumes
+that all commands are recognized. It is structured such that it will
+degrade gracefully when a command is unknown. See the sections above on
+known limitations for details.
+
+
+When a CAN frame is to be sent, the target address is configured, after
+which the frame is sent as a command that consists of the data's hex
+dump::
+
+    >ATSH123
+    OK
+    >DEADBEEF12345678
+    OK
+    >
+
+The above interaction sends the frame "``DE AD BE EF 12 34 56 78``" with
+the 11 bit CAN ID ``0x123``.
+For this to function, the controller must be configured for 11 bit CAN
+ID sending mode (using "``AT PB``", see code or datasheet).
+
+
+Once a frame has been sent and wait-for-reply mode is on (``ATR1``,
+configured on ``listen-only=off``), or when the reply timeout expires and
+the driver sets the controller into monitoring mode (``ATMA``), the ELM327
+will send one line for each received CAN frame, consisting of CAN ID,
+DLC, and data::
+
+    123 8 DEADBEEF12345678
+
+For 29 bit CAN frames, the address format is slightly different, which
+elmcan uses to tell the two apart::
+
+    12 34 56 78 8 DEADBEEF12345678
+
+The ELM327 will receive both 11 and 29 bit frames - the current CAN
+config (``ATPB``) does not matter.
+
+
+If the ELM327's internal UART sending buffer runs full, it will abort
+the monitoring mode, print "BUFFER FULL" and drop back into command
+mode. Note that in this case, unlike with other error messages, the
+error message may appear on the same line as the last (usually
+incomplete) data frame::
+
+    12 34 56 78 8 DEADBEEF123 BUFFER FULL
+
+
+
+Rationale behind the chosen configuration
+------------------------------------------
+
+``AT E1``
+  Echo on
+
+  We need this to be able to get a prompt reliably.
+
+``AT S1``
+  Spaces on
+
+  We need this to distinguish 11/29 bit CAN addresses received.
+
+  Note:
+  We can usually do this using the line length (odd/even),
+  but this fails if the line is not transmitted fully to
+  the host (BUFFER FULL).
+
+``AT D1``
+  DLC on
+
+  We need this to tell the "length" of RTR frames.
+
+
+
+A note on CAN bus termination
+------------------------------
+
+Your adapter may have resistors soldered in which are meant to terminate
+the bus. This is correct when it is plugged into a OBD-II socket, but
+not helpful when trying to tap into the middle of an existing CAN bus.
+
+If communications don't work with the adapter connected, check for the
+termination resistors on its PCB and try removing them.

Documentation/networking/device_drivers/can/index.rst +1 -0

index 58b6e0ad3030..e3f2be735aef 100644
@@ -10,6 +10,7 @@ Contents:
 .. toctree::
    :maxdepth: 2
 
+   elmcan
    freescale/flexcan
 
 .. only::  subproject and html

MAINTAINERS +7 -0

index 3e461db9cd91..7bb266dbffd1 100644
@@ -7064,6 +7064,13 @@ L:       [email protected]
 S:     Maintained
 F:     drivers/net/ethernet/ibm/ehea/
 
+ELM327 CAN NETWORK DRIVER
+M:     Max Staudt <[email protected]>
+L:     [email protected]
+S:     Maintained
+F:     Documentation/networking/device_drivers/can/elmcan.rst
+F:     drivers/net/can/elmcan.c
+
 EM28XX VIDEO4LINUX DRIVER
 M:     Mauro Carvalho Chehab <[email protected]>
 L:     [email protected]

drivers/net/can/Kconfig +17 -0

index fff259247d52..226bd00fc048 100644
@@ -180,6 +180,23 @@ source "drivers/net/can/softing/Kconfig"
 source "drivers/net/can/spi/Kconfig"
 source "drivers/net/can/usb/Kconfig"
 
+config CAN_ELMCAN
+       tristate "Serial / USB serial ELM327 based OBD-II Interfaces (elmcan)"
+       depends on TTY
+       help
+         CAN driver for several 'low cost' OBD-II interfaces based on the
+         ELM327 OBD-II interpreter chip.
+
+         This is a best effort driver - the ELM327 interface was never
+         designed to be used as a standalone CAN interface. However, it can
+         still be used for simple request-response protocols (such as OBD II),
+         and to monitor broadcast messages on a bus (such as in a vehicle).
+
+         Please refer to the documentation for information on how to use it:
+         Documentation/networking/device_drivers/can/elmcan.rst
+
+         If this driver is built as a module, it will be called elmcan.
+
 endif
 
 config CAN_DEBUG_DEVICES

drivers/net/can/Makefile +1 -0

index 1e660afcb61b..c25a0f8a397b 100644
@@ -6,6 +6,7 @@
 obj-$(CONFIG_CAN_VCAN)         += vcan.o
 obj-$(CONFIG_CAN_VXCAN)                += vxcan.o
 obj-$(CONFIG_CAN_SLCAN)                += slcan.o
+obj-$(CONFIG_CAN_ELMCAN)       += elmcan.o
 
 obj-y                          += dev/
 obj-y                          += rcar/

drivers/net/can/elmcan.c new file +58 -0

new file mode 100644
index 000000000000..2d7ebc40a492
@@ -0,0 +1,1250 @@
+// SPDX-License-Identifier: GPL-2.0
+/* ELM327 based CAN interface driver (tty line discipline)
+ *
+ * This driver started as a derivative of linux/drivers/net/can/slcan.c
+ * and my thanks go to the original authors for their inspiration, even
+ * after almost none of their code is left.
+ */
+
+#define pr_fmt(fmt) "[elmcan] " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/ctype.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/if_ether.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/tty.h>
+#include <linux/tty_ldisc.h>
+#include <linux/workqueue.h>
+
+#include <uapi/linux/tty.h>
+
+#include <linux/can.h>
+#include <linux/can/dev.h>
+#include <linux/can/error.h>
+#include <linux/can/led.h>
+#include <linux/can/rx-offload.h>
+
+MODULE_ALIAS_LDISC(N_ELMCAN);
+MODULE_DESCRIPTION("ELM327 based CAN interface");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Max Staudt <[email protected]>");
+
+#define ELM327_NAPI_WEIGHT 4
+
+#define ELM327_SIZE_RXBUF 256
+#define ELM327_SIZE_TXBUF 32
+
+#define ELM327_CAN_CONFIG_SEND_SFF           0x8000
+#define ELM327_CAN_CONFIG_VARIABLE_DLC       0x4000
+#define ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF  0x2000
+#define ELM327_CAN_CONFIG_BAUDRATE_MULT_8_7  0x1000
+
+#define ELM327_DUMMY_CHAR 'y'
+#define ELM327_DUMMY_STRING "y"
+#define ELM327_READY_CHAR '>'
+
+/* Bits in elm->cmds_todo */

drivers/net/can/elmcan.c new file +237 -0

+};
+
+struct elmcan {
+       /* This must be the first member when using alloc_candev() */
+       struct can_priv can;
+
+       struct can_rx_offload offload;
+
+       /* TTY and netdev devices that we're bridging */
+       struct tty_struct       *tty;
+       struct net_device       *dev;
+
+       /* Per-channel lock */
+       spinlock_t              lock;
+
+       /* Keep track of how many things are using this struct.
+        * Once it reaches 0, we are in the process of cleaning up,
+        * and new operations will be cancelled immediately.
+        * Use atomic_t rather than refcount_t because we deliberately
+        * decrement to 0, and refcount_dec() spills a WARN_ONCE in
+        * that case.
+        */
+       atomic_t                refcount;
+
+       /* Stop the channel on hardware failure.
+        * Once this is true, nothing will be sent to the TTY.
+        */
+       bool                    hw_failure;
+
+       /* TTY TX helpers */
+       struct work_struct      tx_work;        /* Flushes TTY TX buffer   */
+       unsigned char           *txbuf;
+       unsigned char           *txhead;        /* Pointer to next TX byte */
+       int                     txleft;         /* Bytes left to TX */
+
+       /* TTY RX helpers */
+       unsigned char rxbuf[ELM327_SIZE_RXBUF];
+       int rxfill;
+
+       /* State machine */
+       enum {
+               ELM_NOTINIT = 0,
+               ELM_GETDUMMYCHAR,
+               ELM_GETPROMPT,
+               ELM_RECEIVING,
+       } state;
+
+       int drop_next_line;
+
+       /* The CAN frame and config the ELM327 is sending/using,
+        * or will send/use after finishing all cmds_todo
+        */
+       struct can_frame can_frame;
+       unsigned short can_config;
+       unsigned long can_bitrate;
+       unsigned char can_bitrate_divisor;
+       int silent_monitoring;
+
+       /* Things we have yet to send */
+       char **next_init_cmd;
+       unsigned long cmds_todo;
+};
+
+/* A lock for all tty->disc_data handled by this ldisc.
+ * This is to prevent a case where tty->disc_data is set to NULL,
+ * yet someone is still trying to dereference it.
+ * Without this, we cannot do a clean shutdown.
+ */
+static DEFINE_SPINLOCK(elmcan_discdata_lock);
+
+static inline void elm327_hw_failure(struct elmcan *elm);
+
+/* Assumes elm->lock taken. */
+static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
+{
+       int actual;
+
+       if (elm->hw_failure)
+               return;
+
+       memcpy(elm->txbuf, buf, len);
+
+       /* Order of next two lines is *very* important.
+        * When we are sending a little amount of data,
+        * the transfer may be completed inside the ops->write()
+        * routine, because it's running with interrupts enabled.
+        * In this case we *never* got WRITE_WAKEUP event,
+        * if we did not request it before write operation.
+        *       14 Oct 1994  Dmitry Gorodchanin.
+        */
+       set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
+       actual = elm->tty->ops->write(elm->tty, elm->txbuf, len);
+       if (actual < 0) {
+               netdev_err(elm->dev,
+                          "Failed to write to tty %s.\n",
+                          elm->tty->name);
+               elm327_hw_failure(elm);
+               return;
+       }
+
+       elm->txleft = len - actual;
+       elm->txhead = elm->txbuf + actual;
+}
+
+/* Take the ELM327 out of almost any state and back into command mode.
+ * We send ELM327_DUMMY_CHAR which will either abort any running
+ * operation, or be echoed back to us in case we're already in command
+ * mode.
+ *
+ * Assumes elm->lock taken.
+ */
+static void elm327_kick_into_cmd_mode(struct elmcan *elm)
+{
+       if (elm->state != ELM_GETDUMMYCHAR && elm->state != ELM_GETPROMPT) {
+               elm327_send(elm, ELM327_DUMMY_STRING, 1);
+
+               elm->state = ELM_GETDUMMYCHAR;
+       }
+}
+
+/* Schedule a CAN frame and necessary config changes to be sent to the TTY.
+ *
+ * Assumes elm->lock taken.
+ */
+static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
+{
+       /* Schedule any necessary changes in ELM327's CAN configuration */
+       if (elm->can_frame.can_id != frame->can_id) {
+               /* Set the new CAN ID for transmission. */
+               if ((frame->can_id & CAN_EFF_FLAG)
+                   ^ (elm->can_frame.can_id & CAN_EFF_FLAG)) {
+                       elm->can_config = (frame->can_id & CAN_EFF_FLAG
+                                               ? 0
+                                               : ELM327_CAN_CONFIG_SEND_SFF)
+                                       | ELM327_CAN_CONFIG_VARIABLE_DLC
+                                       | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
+                                       | elm->can_bitrate_divisor;
+
+                       set_bit(TODO_CAN_CONFIG, &elm->cmds_todo);
+               }
+
+               if (frame->can_id & CAN_EFF_FLAG) {
+                       clear_bit(TODO_CANID_11BIT, &elm->cmds_todo);
+                       set_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo);
+                       set_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo);
+               } else {
+                       set_bit(TODO_CANID_11BIT, &elm->cmds_todo);
+                       clear_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo);
+                       clear_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo);
+               }
+       }
+
+       /* Schedule the CAN frame itself. */
+       elm->can_frame = *frame;
+       set_bit(TODO_CAN_DATA, &elm->cmds_todo);
+
+       elm327_kick_into_cmd_mode(elm);
+}
+
+/* ELM327 initialization sequence.
+ *
+ * Assumes elm->lock taken.
+ */
+static char *elm327_init_script[] = {
+       "AT WS\r",        /* v1.0: Warm Start */
+       "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
+       "AT M0\r",        /* v1.0: Memory Off */
+       "AT AL\r",        /* v1.0: Allow Long messages */
+       "AT BI\r",        /* v1.0: Bypass Initialization */
+       "AT CAF0\r",      /* v1.0: CAN Auto Formatting Off */
+       "AT CFC0\r",      /* v1.0: CAN Flow Control Off */
+       "AT CF 000\r",    /* v1.0: Reset CAN ID Filter */
+       "AT CM 000\r",    /* v1.0: Reset CAN ID Mask */
+       "AT E1\r",        /* v1.0: Echo On */
+       "AT H1\r",        /* v1.0: Headers On */
+       "AT L0\r",        /* v1.0: Linefeeds Off */
+       "AT SH 7DF\r",    /* v1.0: Set CAN sending ID to 0x7df */
+       "AT ST FF\r",     /* v1.0: Set maximum Timeout for response after TX */
+       "AT AT0\r",       /* v1.2: Adaptive Timing Off */
+       "AT D1\r",        /* v1.3: Print DLC On */
+       "AT S1\r",        /* v1.3: Spaces On */
+       "AT TP B\r",      /* v1.0: Try Protocol B */
+       NULL
+};
+
+static void elm327_init(struct elmcan *elm)
+{
+       elm->state = ELM_NOTINIT;
+       elm->can_frame.can_id = 0x7df;
+       elm->rxfill = 0;
+       elm->drop_next_line = 0;
+
+       /* We can only set the bitrate as a fraction of 500000.
+        * The bit timing constants in elmcan_bittiming_const will
+        * limit the user to the right values.
+        */
+       elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
+       elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
+                       | ELM327_CAN_CONFIG_VARIABLE_DLC
+                       | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
+                       | elm->can_bitrate_divisor;
+
+       /* Configure ELM327 and then start monitoring */
+       elm->next_init_cmd = &elm327_init_script[0];
+       set_bit(TODO_INIT, &elm->cmds_todo);
+       set_bit(TODO_SILENT_MONITOR, &elm->cmds_todo);
+       set_bit(TODO_RESPONSES, &elm->cmds_todo);
+       set_bit(TODO_CAN_CONFIG, &elm->cmds_todo);
+
+       elm327_kick_into_cmd_mode(elm);
+}
+
+/* Assumes elm->lock taken. */
+static void elm327_feed_frame_to_netdev(struct elmcan *elm,
+                                       const struct can_frame *frame)
+{
+       struct can_frame *cf;
+       struct sk_buff *skb;
+
+       if (!netif_running(elm->dev))
+               return;
+
+       skb = alloc_can_skb(elm->dev, &cf);
+
+       if (!skb)
+               return;
+
+       memcpy(cf, frame, sizeof(struct can_frame));
+
+       /* Queue for NAPI pickup.
+        * rx-offload will update stats and LEDs for us.
+        */
+       if (can_rx_offload_queue_tail(&elm->offload, skb))
+               elm->dev->stats.rx_fifo_errors++;
+
+       /* Wake NAPI */
+       can_rx_offload_irq_finish(&elm->offload);

drivers/net/can/elmcan.c new file +61 -0

+}
+
+/* Assumes elm->lock taken. */
+static void elm327_parse_error(struct elmcan *elm, size_t len)
+{
+       struct can_frame frame;
+
+       memset(&frame, 0, sizeof(frame));
+       frame.can_id = CAN_ERR_FLAG;
+       frame.can_dlc = CAN_ERR_DLC;
+
+       /* Filter possible error messages based on length of RX'd line */
+       if (!_len_memstrcmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
+               netdev_err(elm->dev,
+                          "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
+       } else if (!_len_memstrcmp(elm->rxbuf, len, "BUFFER FULL")) {
+               /* This will only happen if the last data line was complete.
+                * Otherwise, elm327_parse_frame() will heuristically
+                * emit this kind of error frame instead.
+                */
+               frame.can_id |= CAN_ERR_CRTL;
+               frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
+       } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS ERROR")) {
+               frame.can_id |= CAN_ERR_BUSERROR;
+       } else if (!_len_memstrcmp(elm->rxbuf, len, "CAN ERROR")) {
+               frame.can_id |= CAN_ERR_PROT;
+       } else if (!_len_memstrcmp(elm->rxbuf, len, "<RX ERROR")) {
+               frame.can_id |= CAN_ERR_PROT;
+       } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS BUSY")) {
+               frame.can_id |= CAN_ERR_PROT;
+               frame.data[2] = CAN_ERR_PROT_OVERLOAD;
+       } else if (!_len_memstrcmp(elm->rxbuf, len, "FB ERROR")) {
+               frame.can_id |= CAN_ERR_PROT;
+               frame.data[2] = CAN_ERR_PROT_TX;
+       } else if (len == 5 && !_memstrcmp(elm->rxbuf, "ERR")) {
+               /* ERR is followed by two digits, hence line length 5 */
+               netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
+                          elm->rxbuf[3], elm->rxbuf[4]);
+               frame.can_id |= CAN_ERR_CRTL;
+       } else {
+               /* Something else has happened.
+                * Maybe garbage on the UART line.
+                * Emit a generic error frame.
+                */
+       }
+
+       elm327_feed_frame_to_netdev(elm, &frame);
+}
+
+/* Parse CAN frames coming as ASCII from ELM327.
+ * They can be of various formats:
+ *
+ * 29-bit ID (EFF):  12 34 56 78 D PL PL PL PL PL PL PL PL
+ * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
+ *
+ * where D = DLC, PL = payload byte
+ *
+ * Instead of a payload, RTR indicates a remote request.
+ *
+ * We will use the spaces and line length to guess the format.
+ *

drivers/net/can/elmcan.c new file +24 -0

+
+       /* Find first non-hex and non-space character:
+        *  - In the simplest case, there is none.
+        *  - For RTR frames, 'R' is the first non-hex character.
+        *  - An error message may replace the end of the data line.
+        */
+       for (hexlen = 0; hexlen <= len; hexlen++) {
+               if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
+                   elm->rxbuf[hexlen] != ' ') {
+                       break;
+               }
+       }
+
+       /* Sanity check whether the line is really a clean hexdump,
+        * or terminated by an error message, or contains garbage.
+        */
+       if (hexlen < len &&
+           !isdigit(elm->rxbuf[hexlen]) &&
+           !isupper(elm->rxbuf[hexlen]) &&
+           '<' != elm->rxbuf[hexlen] &&
+           ' ' != elm->rxbuf[hexlen]) {
+               /* The line is likely garbled anyway, so bail.
+                * The main code will restart listening.
+                */

drivers/net/can/elmcan.c new file +30 -0

+               frame.can_id = CAN_EFF_FLAG;
+               datastart = 14;
+       } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
+               frame.can_id = 0;
+               datastart = 6;
+       } else {
+               /* This is not a well-formatted data line.
+                * Assume it's an error message.
+                */
+               return -ENODATA;
+       }
+
+       if (hexlen < datastart) {
+               /* The line is too short to be a valid frame hex dump.
+                * Something interrupted the hex dump or it is invalid.
+                */
+               return -ENODATA;
+       }
+
+       /* From here on all chars up to buf[hexlen] are hex or spaces,
+        * at well-defined offsets.
+        */
+
+       /* Read CAN data length */
+       frame.can_dlc = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
+
+       /* Read CAN ID */
+       if (frame.can_id & CAN_EFF_FLAG) {
+               frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
+                             | (hex_to_bin(elm->rxbuf[1]) << 24)

drivers/net/can/elmcan.c new file +23 -0

+       }
+
+       /* Check for RTR frame */
+       if (elm->rxfill >= hexlen + 3 &&
+           !_memstrcmp(&elm->rxbuf[hexlen], "RTR")) {
+               frame.can_id |= CAN_RTR_FLAG;
+       }
+
+       /* Is the line long enough to hold the advertised payload?
+        * Note: RTR frames have a DLC, but no actual payload.
+        */
+       if (!(frame.can_id & CAN_RTR_FLAG) &&
+           (hexlen < frame.can_dlc * 3 + datastart)) {
+               /* Incomplete frame. */
+
+               /* Probably the ELM327's RS232 TX buffer was full.
+                * Emit an error frame and exit.
+                */
+               frame.can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
+               frame.can_dlc = CAN_ERR_DLC;
+               frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
+               elm327_feed_frame_to_netdev(elm, &frame);
+

drivers/net/can/elmcan.c new file +19 -0

+               frame.data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
+                             | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
+       }
+
+       /* Feed the frame to the network layer. */
+       elm327_feed_frame_to_netdev(elm, &frame);
+
+       return 0;
+}
+
+/* Assumes elm->lock taken. */
+static void elm327_parse_line(struct elmcan *elm, size_t len)
+{
+       /* Skip empty lines */
+       if (!len)
+               return;
+
+       /* Skip echo lines */
+       if (elm->drop_next_line) {

drivers/net/can/elmcan.c new file +108 -0

+                       /* Parse an error line. */
+                       elm327_parse_error(elm, len);
+
+                       /* Start afresh. */
+                       elm327_kick_into_cmd_mode(elm);
+               }
+               break;
+       default:
+               break;
+       }
+}
+
+/* Assumes elm->lock taken. */
+static void elm327_handle_prompt(struct elmcan *elm)
+{
+       struct can_frame *frame = &elm->can_frame;
+       char local_txbuf[20];
+
+       if (!elm->cmds_todo) {
+               /* Enter CAN monitor mode */
+               elm327_send(elm, "ATMA\r", 5);
+               elm->state = ELM_RECEIVING;
+
+               return;
+       }
+
+       /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
+       if (test_bit(TODO_INIT, &elm->cmds_todo)) {
+               strcpy(local_txbuf, *elm->next_init_cmd);
+
+               elm->next_init_cmd++;
+               if (!(*elm->next_init_cmd)) {
+                       clear_bit(TODO_INIT, &elm->cmds_todo);
+                       /* Init finished. */
+               }
+
+       } else if (test_and_clear_bit(TODO_SILENT_MONITOR, &elm->cmds_todo)) {
+               sprintf(local_txbuf, "ATCSM%i\r",
+                       !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
+
+       } else if (test_and_clear_bit(TODO_RESPONSES, &elm->cmds_todo)) {
+               sprintf(local_txbuf, "ATR%i\r",
+                       !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
+
+       } else if (test_and_clear_bit(TODO_CAN_CONFIG, &elm->cmds_todo)) {
+               sprintf(local_txbuf, "ATPC\r");
+               set_bit(TODO_CAN_CONFIG_PART2, &elm->cmds_todo);
+
+       } else if (test_and_clear_bit(TODO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
+               sprintf(local_txbuf, "ATPB%04X\r",
+                       elm->can_config);
+
+       } else if (test_and_clear_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
+               sprintf(local_txbuf, "ATCP%02X\r",
+                       (frame->can_id & CAN_EFF_MASK) >> 24);
+
+       } else if (test_and_clear_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo)) {
+               sprintf(local_txbuf, "ATSH%06X\r",
+                       frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
+
+       } else if (test_and_clear_bit(TODO_CANID_11BIT, &elm->cmds_todo)) {
+               sprintf(local_txbuf, "ATSH%03X\r",
+                       frame->can_id & CAN_SFF_MASK);
+
+       } else if (test_and_clear_bit(TODO_CAN_DATA, &elm->cmds_todo)) {
+               if (frame->can_id & CAN_RTR_FLAG) {
+                       /* Send an RTR frame. Their DLC is fixed.
+                        * Some chips don't send them at all.
+                        */
+                       sprintf(local_txbuf, "ATRTR\r");
+               } else {
+                       /* Send a regular CAN data frame */
+                       int i;
+
+                       for (i = 0; i < frame->can_dlc; i++) {
+                               sprintf(&local_txbuf[2 * i], "%02X",
+                                       frame->data[i]);
+                       }
+
+                       sprintf(&local_txbuf[2 * i], "\r");
+               }
+
+               elm->drop_next_line = 1;
+               elm->state = ELM_RECEIVING;
+       }
+
+       elm327_send(elm, local_txbuf, strlen(local_txbuf));
+}
+
+static bool elm327_is_ready_char(char c)
+{
+       /* Bits 0xc0 are sometimes set (randomly), hence the mask.
+        * Probably bad hardware.
+        */
+       return (c & 0x3f) == ELM327_READY_CHAR;
+}
+
+/* Assumes elm->lock taken. */
+static void elm327_drop_bytes(struct elmcan *elm, size_t i)
+{
+       memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
+       elm->rxfill -= i;
+}
+
+/* Assumes elm->lock taken. */
+static void elm327_parse_rxbuf(struct elmcan *elm)
+{
+       size_t len;

drivers/net/can/elmcan.c new file +21 -0

+
+               for (i = 0; i < elm->rxfill; i++) {
+                       if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
+                               elm327_send(elm, "\r", 1);
+                               elm->state = ELM_GETPROMPT;
+                               i++;
+                               break;
+                       } else if (elm327_is_ready_char(elm->rxbuf[i])) {
+                               elm327_send(elm, ELM327_DUMMY_STRING, 1);
+                               i++;
+                               break;
+                       }
+               }
+
+               elm327_drop_bytes(elm, i);
+
+               break;
+       }
+
+       case ELM_GETPROMPT:
+               /* Wait for '>' */

drivers/net/can/elmcan.c new file +41 -0

+                    len++) {
+                       /* empty loop */
+               }
+
+               if (len == ELM327_SIZE_RXBUF) {
+                       /* Line exceeds buffer. It's probably all garbage.
+                        * Did we even connect at the right baud rate?
+                        */
+                       netdev_err(elm->dev,
+                                  "RX buffer overflow. Faulty ELM327 or UART?\n");
+                       elm327_hw_failure(elm);
+                       break;
+               } else if (len == elm->rxfill) {
+                       if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
+                               /* The ELM327's AT ST response timeout ran out,
+                                * so we got a prompt.
+                                * Clear RX buffer and restart listening.
+                                */
+                               elm->rxfill = 0;
+
+                               elm327_handle_prompt(elm);
+                               break;
+                       }
+
+                       /* No <CR> found - we haven't received a full line yet.
+                        * Wait for more data.
+                        */
+                       break;
+               }
+
+               /* We have a full line to parse. */
+               elm327_parse_line(elm, len);
+
+               /* Remove parsed data from RX buffer. */
+               elm327_drop_bytes(elm, len + 1);
+
+               /* More data to parse? */
+               if (elm->rxfill)
+                       elm327_parse_rxbuf(elm);
+       }
+}

drivers/net/can/elmcan.c new file +75 -0

+
+static int elmcan_netdev_open(struct net_device *dev)
+{
+       struct elmcan *elm = netdev_priv(dev);
+       int err;
+
+       spin_lock_bh(&elm->lock);
+       if (elm->hw_failure) {
+               netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
+               spin_unlock_bh(&elm->lock);
+               return -EIO;
+       }
+
+       if (!elm->tty) {
+               spin_unlock_bh(&elm->lock);
+               return -ENODEV;
+       }
+
+       /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
+       err = open_candev(dev);
+       if (err) {
+               spin_unlock_bh(&elm->lock);
+               return err;
+       }
+
+       elm327_init(elm);
+       spin_unlock_bh(&elm->lock);
+
+       elm->offload.mailbox_read = elmcan_mailbox_read;
+       err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
+       if (err) {
+               close_candev(dev);
+               return err;
+       }
+
+       can_rx_offload_enable(&elm->offload);
+
+       can_led_event(dev, CAN_LED_EVENT_OPEN);
+       elm->can.state = CAN_STATE_ERROR_ACTIVE;
+       netif_start_queue(dev);
+
+       return 0;
+}
+
+static int elmcan_netdev_close(struct net_device *dev)
+{
+       struct elmcan *elm = netdev_priv(dev);
+
+       netif_stop_queue(dev);
+
+       spin_lock_bh(&elm->lock);
+       if (elm->tty) {
+               /* Interrupt whatever we're doing right now */
+               elm327_send(elm, ELM327_DUMMY_STRING, 1);
+
+               /* Clear the wakeup bit, as the netdev will be down and thus
+                * the wakeup handler won't clear it
+                */
+               clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
+
+               spin_unlock_bh(&elm->lock);
+
+               flush_work(&elm->tx_work);
+       } else {
+               spin_unlock_bh(&elm->lock);
+       }
+
+       can_rx_offload_disable(&elm->offload);
+       elm->can.state = CAN_STATE_STOPPED;
+       can_rx_offload_del(&elm->offload);
+       close_candev(dev);
+       can_led_event(dev, CAN_LED_EVENT_STOP);
+
+       return 0;
+}

drivers/net/can/elmcan.c new file +15 -0

+
+       /* BHs are already disabled, so no spin_lock_bh().
+        * See Documentation/networking/netdevices.txt
+        */
+       spin_lock(&elm->lock);
+
+       /* We shouldn't get here after a hardware fault:
+        * can_bus_off() calls netif_carrier_off()
+        */
+       WARN_ON_ONCE(elm->hw_failure);
+
+       if (!elm->tty ||
+           elm->hw_failure ||
+           elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
+               spin_unlock(&elm->lock);

drivers/net/can/elmcan.c new file +383 -0

+
+       can_led_event(dev, CAN_LED_EVENT_TX);
+
+out:
+       kfree_skb(skb);
+       return NETDEV_TX_OK;
+}
+
+static const struct net_device_ops elmcan_netdev_ops = {
+       .ndo_open       = elmcan_netdev_open,
+       .ndo_stop       = elmcan_netdev_close,
+       .ndo_start_xmit = elmcan_netdev_start_xmit,
+       .ndo_change_mtu = can_change_mtu,
+};
+
+/* Get a reference to our struct, taking into account locks/refcounts.
+ * This is to ensure ordering in case we are shutting down, and to ensure
+ * there is a refcount at all (otherwise tty->disc_data may be freed and
+ * before we increment the refcount).
+ * Use this for anything that can race against elmcan_ldisc_close().
+ */
+static struct elmcan *get_elm(struct tty_struct *tty)
+{
+       struct elmcan *elm;
+       bool got_ref;
+
+       spin_lock_bh(&elmcan_discdata_lock);
+       elm = (struct elmcan *)tty->disc_data;
+
+       if (!elm) {
+               spin_unlock_bh(&elmcan_discdata_lock);
+               return NULL;
+       }
+
+       got_ref = atomic_inc_not_zero(&elm->refcount);
+       spin_unlock_bh(&elmcan_discdata_lock);
+
+       if (!got_ref)
+               return NULL;
+
+       return elm;
+}
+
+static void put_elm(struct elmcan *elm)
+{
+       atomic_dec(&elm->refcount);
+}
+
+static bool elmcan_is_valid_rx_char(char c)
+{
+       return (isdigit(c) ||
+               isupper(c) ||
+               c == ELM327_DUMMY_CHAR ||
+               c == ELM327_READY_CHAR ||
+               c == '<' ||
+               c == 'a' ||
+               c == 'b' ||
+               c == 'v' ||
+               c == '.' ||
+               c == '?' ||
+               c == '\r' ||
+               c == ' ');
+}
+
+/* Handle incoming ELM327 ASCII data.
+ * This will not be re-entered while running, but other ldisc
+ * functions may be called in parallel.
+ */
+static void elmcan_ldisc_rx(struct tty_struct *tty,
+                           const unsigned char *cp, const char *fp, int count)
+{
+       struct elmcan *elm = get_elm(tty);
+
+       if (!elm)
+               return;
+
+       spin_lock_bh(&elm->lock);
+
+       if (elm->hw_failure)
+               goto out;
+
+       while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
+               if (fp && *fp++) {
+                       netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
+
+                       elm327_hw_failure(elm);
+
+                       goto out;
+               }
+
+               /* Ignore NUL characters, which the PIC microcontroller may
+                * inadvertently insert due to a known hardware bug.
+                * See ELM327 documentation, which refers to a Microchip PIC
+                * bug description.
+                */
+               if (*cp != 0) {
+                       /* Check for stray characters on the UART line.
+                        * Likely caused by bad hardware.
+                        */
+                       if (!elmcan_is_valid_rx_char(*cp)) {
+                               netdev_err(elm->dev,
+                                          "Received illegal character %02x.\n",
+                                          *cp);
+                               elm327_hw_failure(elm);
+
+                               goto out;
+                       }
+
+                       elm->rxbuf[elm->rxfill++] = *cp;
+               }
+
+               cp++;
+       }
+
+       if (count >= 0) {
+               netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
+
+               elm327_hw_failure(elm);
+
+               goto out;
+       }
+
+       elm327_parse_rxbuf(elm);
+
+out:
+       spin_unlock_bh(&elm->lock);
+       put_elm(elm);
+}
+
+/* Write out remaining transmit buffer.
+ * Scheduled when TTY is writable.
+ */
+static void elmcan_ldisc_tx_worker(struct work_struct *work)
+{
+       /* No need to use get_elm() here, as we'll always flush workers
+        * before destroying the elmcan object.
+        */
+       struct elmcan *elm = container_of(work, struct elmcan, tx_work);
+       ssize_t actual;
+
+       spin_lock_bh(&elm->lock);
+       if (elm->hw_failure) {
+               spin_unlock_bh(&elm->lock);
+               return;
+       }
+
+       if (!elm->tty || !netif_running(elm->dev)) {
+               spin_unlock_bh(&elm->lock);
+               return;
+       }
+
+       if (elm->txleft <= 0)  {
+               /* Our TTY write buffer is empty:
+                * Allow netdev to hand us another packet
+                */
+               clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
+               spin_unlock_bh(&elm->lock);
+               netif_wake_queue(elm->dev);
+               return;
+       }
+
+       actual = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
+       if (actual < 0) {
+               netdev_err(elm->dev,
+                          "Failed to write to tty %s.\n",
+                          elm->tty->name);
+               elm327_hw_failure(elm);
+               spin_unlock_bh(&elm->lock);
+               return;
+       }
+
+       elm->txleft -= actual;
+       elm->txhead += actual;
+       spin_unlock_bh(&elm->lock);
+}
+
+/* Called by the driver when there's room for more data. */
+static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
+{
+       struct elmcan *elm = get_elm(tty);
+
+       if (!elm)
+               return;
+
+       schedule_work(&elm->tx_work);
+
+       put_elm(elm);
+}
+
+/* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
+ * or 7/8 of that. Divisors are 1 to 64.
+ * Currently we don't implement support for 7/8 rates.
+ */
+static const u32 elmcan_bitrate_const[64] = {
+        7812,  7936,  8064,  8196,  8333,  8474,  8620,  8771,
+        8928,  9090,  9259,  9433,  9615,  9803, 10000, 10204,
+       10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
+       12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
+       15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
+       20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
+       31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
+       62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
+};
+
+/* Dummy needed to use bitrate_const */
+static int elmcan_do_set_bittiming(struct net_device *netdev)
+{
+       return 0;
+}
+
+static int elmcan_ldisc_open(struct tty_struct *tty)
+{
+       struct net_device *dev;
+       struct elmcan *elm;
+       int err;
+
+       if (!capable(CAP_NET_ADMIN))
+               return -EPERM;
+
+       if (!tty->ops->write)
+               return -EOPNOTSUPP;
+
+       dev = alloc_candev(sizeof(struct elmcan), 0);
+       if (!dev)
+               return -ENFILE;
+       elm = netdev_priv(dev);
+
+       elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
+       if (!elm->txbuf) {
+               err = -ENOMEM;
+               goto out_err;
+       }
+
+       /* Configure TTY interface */
+       tty->receive_room = 65536; /* We don't flow control */
+       elm->txleft = 0; /* Clear TTY TX buffer */
+       spin_lock_init(&elm->lock);
+       atomic_set(&elm->refcount, 1);
+       INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
+
+       /* Configure CAN metadata */
+       elm->can.state = CAN_STATE_STOPPED;
+       elm->can.bitrate_const = elmcan_bitrate_const;
+       elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
+       elm->can.do_set_bittiming = elmcan_do_set_bittiming;
+       elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
+
+       /* Configure netdev interface */
+       elm->dev = dev;
+       dev->netdev_ops = &elmcan_netdev_ops;
+
+       /* Mark ldisc channel as alive */
+       elm->tty = tty;
+       tty->disc_data = elm;
+
+       devm_can_led_init(elm->dev);
+
+       /* Let 'er rip */
+       err = register_candev(elm->dev);
+       if (err)
+               goto out_err;
+
+       netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
+
+       return 0;
+
+out_err:
+       kfree(elm->txbuf);
+       free_candev(elm->dev);
+       return err;
+}
+
+/* Close down an elmcan channel.
+ * This means flushing out any pending queues, and then returning.
+ * This call is serialized against other ldisc functions:
+ * Once this is called, no other ldisc function of ours is entered.
+ *
+ * We also use this function for a hangup event.
+ */
+static void elmcan_ldisc_close(struct tty_struct *tty)
+{
+       struct elmcan *elm = get_elm(tty);
+
+       if (!elm)
+               return;
+
+       /* unregister_netdev() calls .ndo_stop() so we don't have to. */
+       unregister_candev(elm->dev);
+
+       /* Decrease the refcount twice, once for our own get_elm(),
+        * and once to remove the count of 1 that we set in _open().
+        * Once it reaches 0, we can safely destroy it.
+        */
+       put_elm(elm);
+       put_elm(elm);
+
+       while (atomic_read(&elm->refcount) > 0)
+               msleep_interruptible(10);
+
+       /* At this point, all ldisc calls to us have become no-ops. */
+
+       flush_work(&elm->tx_work);
+
+       /* Mark channel as dead */
+       spin_lock_bh(&elm->lock);
+       tty->disc_data = NULL;
+       elm->tty = NULL;
+       spin_unlock_bh(&elm->lock);
+
+       netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
+
+       kfree(elm->txbuf);
+       free_candev(elm->dev);
+}
+
+static void elmcan_ldisc_hangup(struct tty_struct *tty)
+{
+       elmcan_ldisc_close(tty);
+}
+
+static int elmcan_ldisc_ioctl(struct tty_struct *tty,
+                             unsigned int cmd, unsigned long arg)
+{
+       struct elmcan *elm = get_elm(tty);
+       unsigned int tmp;
+
+       if (!elm)
+               return -EINVAL;
+
+       switch (cmd) {
+       case SIOCGIFNAME:
+               tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
+               if (copy_to_user((void __user *)arg, elm->dev->name, tmp)) {
+                       put_elm(elm);
+                       return -EFAULT;
+               }
+
+               put_elm(elm);
+               return 0;
+
+       case SIOCSIFHWADDR:
+               put_elm(elm);
+               return -EINVAL;
+
+       default:
+               put_elm(elm);
+               return tty_mode_ioctl(tty, cmd, arg);
+       }
+}
+
+static struct tty_ldisc_ops elmcan_ldisc = {
+       .owner          = THIS_MODULE,
+       .name           = "elmcan",
+       .num            = N_ELMCAN,
+       .receive_buf    = elmcan_ldisc_rx,
+       .write_wakeup   = elmcan_ldisc_tx_wakeup,
+       .open           = elmcan_ldisc_open,
+       .close          = elmcan_ldisc_close,
+       .hangup         = elmcan_ldisc_hangup,
+       .ioctl          = elmcan_ldisc_ioctl,
+};
+
+static int __init elmcan_init(void)
+{
+       int status;
+
+       status = tty_register_ldisc(&elmcan_ldisc);
+       if (status)
+               pr_err("Can't register line discipline\n");
+
+       return status;
+}
+
+static void __exit elmcan_exit(void)
+{
+       /* This will only be called when all channels have been closed by
+        * userspace - tty_ldisc.c takes care of the module's refcount.
+        */
+       tty_unregister_ldisc(&elmcan_ldisc);
+}
+
+module_init(elmcan_init);
+module_exit(elmcan_exit);

include/uapi/linux/tty.h +2 -2

index 9d0f06bfbac3..bd034d0511f6 100644
@@ -38,8 +38,9 @@
 #define N_NULL         27      /* Null ldisc used for error handling */
 #define N_MCTP         28      /* MCTP-over-serial */
 #define N_DEVELOPMENT  29      /* Manual out-of-tree testing */
+#define N_ELMCAN       30      /* Serial / USB serial OBD-II Interfaces */
 
 /* Always the newest line discipline + 1 */
-#define NR_LDISCS      30
+#define NR_LDISCS      31
 
 #endif /* _UAPI_LINUX_TTY_H */
--

2.30.2

Hi Max, this is a partial review.

drivers/net/can/elmcan.c line 68

Quoted 11 lines

drivers/net/can/elmcan.c new file +11 -0

+/* Bits in elm->cmds_todo */
+enum ELM_TODO {
+       TODO_CAN_DATA = 0,
+       TODO_CANID_11BIT,
+       TODO_CANID_29BIT_LOW,
+       TODO_CANID_29BIT_HIGH,
+       TODO_CAN_CONFIG_PART2,
+       TODO_CAN_CONFIG,
+       TODO_RESPONSES,
+       TODO_SILENT_MONITOR,
+       TODO_INIT  

Nitpick but the TODO name is bugging me. What does this acronym mean? Is it possible to change this so it doesn't look like a FIXME tag?

drivers/net/can/elmcan.c line 321

Quoted 6 lines

drivers/net/can/elmcan.c new file +6 -0

+       frame.can_id = CAN_ERR_FLAG;
+       frame.can_dlc = CAN_ERR_DLC;
+       frame.data[5] = 'R';
+       frame.data[6] = 'I';
+       frame.data[7] = 'P';
+       elm327_feed_frame_to_netdev(elm, &frame);  

There is a framework to notify a bus off. Refer to:
https://elixir.bootlin.com/linux/latest/source/drivers/net/can/usb/etas_es58x/es58x_core.c#L815

drivers/net/can/elmcan.c line 332

Quoted 4 lines

drivers/net/can/elmcan.c new file +4 -0

+/* Compare a buffer to a fixed string */
+static inline int _memstrcmp(const u8 *mem, const char *str)
+{
+       return memcmp(mem, str, strlen(str));  

strcpy()?
Did you check for buffer overflow?

drivers/net/can/elmcan.c line 450

Quoted 9 lines

(quoted diff) +2 -0

+
+       /* Use spaces in CAN ID to distinguish 29 or 11 bit address

length.

drivers/net/can/elmcan.c new file +6 -0

+        * No out-of-bounds access:
+        * We use the fact that we can always read from elm->rxbuf.
+        */
+       if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
+           elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
+           elm->rxbuf[13] == ' ') {  

Define an inline function elm327_is_eff().

Quoted 4 lines

drivers/net/can/elmcan.c new file +4 -0

+       /* Read CAN ID */
+       if (frame.can_id & CAN_EFF_FLAG) {
+               frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
+                             | (hex_to_bin(elm->rxbuf[1]) << 24)

drivers/net/can/elmcan.c line 490

Quoted 10 lines

drivers/net/can/elmcan.c new file +10 -0

+                             | (hex_to_bin(elm->rxbuf[3]) << 20)
+                             | (hex_to_bin(elm->rxbuf[4]) << 16)
+                             | (hex_to_bin(elm->rxbuf[6]) << 12)
+                             | (hex_to_bin(elm->rxbuf[7]) << 8)
+                             | (hex_to_bin(elm->rxbuf[9]) << 4)
+                             | (hex_to_bin(elm->rxbuf[10]) << 0);
+       } else {
+               frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
+                             | (hex_to_bin(elm->rxbuf[1]) << 4)
+                             | (hex_to_bin(elm->rxbuf[2]) << 0);  

hex2bin()?

drivers/net/can/elmcan.c line 523

Quoted 2 lines

drivers/net/can/elmcan.c new file +2 -0

+       /* Parse the data nibbles. */
+       for (i = 0; i < frame.can_dlc; i++) {  

frame.can_dlc is deprecated. Use frame.len instead.

Quoted 5 lines

drivers/net/can/elmcan.c new file +4 -0

+       case ELM_RECEIVING:
+               /* Find <CR> delimiting feedback lines. */
+               for (len = 0;
+                    (len < elm->rxfill) && (elm->rxbuf[len] !=

'\r');

Did you use ./script/checkpath?

Quoted 6 lines

(quoted diff) +2 -0

+/* Dummy needed to use can_rx_offload */
+static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload

*offload,
+ unsigned int n, u32
*timestamp,
+ bool drop)

drivers/net/can/elmcan.c line 752

Quoted 5 lines

(quoted diff) +2 -0

+{
+       WARN_ON_ONCE(1); /* This function is a dummy, so don't call

it! */ +

drivers/net/can/elmcan.c new file +2 -0

+       return ERR_PTR(-ENOBUFS);
+}  

Could you elaborate on why you need can_rx_offload if the mailbox feature is not needed?

drivers/net/can/elmcan.c line 837

Quoted 9 lines

drivers/net/can/elmcan.c new file +9 -0

+/* Send a can_frame to a TTY. */
+static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
+                                           struct net_device *dev)
+{
+       struct elmcan *elm = netdev_priv(dev);
+       struct can_frame *frame = (struct can_frame *)skb->data;
+
+       if (skb->len != sizeof(struct can_frame))
+               goto out;  

Isn’t this aleardy guaranteed by the upper layers?

drivers/net/can/elmcan.c line 842

Quoted 4 lines

drivers/net/can/elmcan.c new file +4 -0

+       if (!netif_running(dev))  {
+               netdev_warn(elm->dev, "xmit: iface is down.\n");
+               goto out;
+       }  

Even if this check succeeds, interface might still go down at the next cycle. What is the purpose of checking if interface is up here?

Thanks a lot Vincent for your review!

Most points are self explanatory, for the others I've added replies below.

Quoted 16 lines · On Tue, 8 Mar 2022 16:01:12 +0900 Vincent Mailhol <[email protected]>…

Hi Max, this is a partial review.

drivers/net/can/elmcan.c line 68

Quoted 11 lines

drivers/net/can/elmcan.c new file +11 -0

+/* Bits in elm->cmds_todo */
+enum ELM_TODO {
+       TODO_CAN_DATA = 0,
+       TODO_CANID_11BIT,
+       TODO_CANID_29BIT_LOW,
+       TODO_CANID_29BIT_HIGH,
+       TODO_CAN_CONFIG_PART2,
+       TODO_CAN_CONFIG,
+       TODO_RESPONSES,
+       TODO_SILENT_MONITOR,
+       TODO_INIT

Nitpick but the TODO name is bugging me. What does this acronym mean? Is it possible to change this so it doesn't look like a FIXME tag?

Good point, I'll change it.

It's an ordered list of things to send next to the adapter.

For
example, whenever the sending CAN ID needs to be changed, the relevant TODO_* bits are set, and the new CAN ID is sent down the UART before a payload (*_DATA) is ever sent.

Quoted 8 lines

Quoted 7 lines

drivers/net/can/elmcan.c new file +6 -0

+       frame.can_id = CAN_ERR_FLAG;
+       frame.can_dlc = CAN_ERR_DLC;
+       frame.data[5] = 'R';
+       frame.data[6] = 'I';
+       frame.data[7] = 'P';
+       elm327_feed_frame_to_netdev(elm, &frame);

Quoted 2 lines

There is a framework to notify a bus off. Refer to:
https://elixir.bootlin.com/linux/latest/source/drivers/net/can/usb/etas_es58x/es58x_core.c#L815

Thanks, will do.

Quoted 6 lines

drivers/net/can/elmcan.c line 332

Quoted 4 lines

drivers/net/can/elmcan.c new file +4 -0

+/* Compare a buffer to a fixed string */
+static inline int _memstrcmp(const u8 *mem, const char *str)
+{
+       return memcmp(mem, str, strlen(str));

strcpy()?

Quoted 1 line

Did you check for buffer overflow?

There is no buffer overflow, as this only ever takes string constants as *str. The compiler figures out the strlen() and can generate an optimised memcmp() for this given string length.

It's the caller's job to ensure that *mem is large enough.

Quoted 10 lines

Quoted 9 lines

(quoted diff) +2 -0

+
+       /* Use spaces in CAN ID to distinguish 29 or 11 bit address

length.

drivers/net/can/elmcan.c new file +6 -0

+        * No out-of-bounds access:
+        * We use the fact that we can always read from elm->rxbuf.
+        */
+       if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
+           elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
+           elm->rxbuf[13] == ' ') {

Quoted 1 line

Define an inline function elm327_is_eff().

It would only be used this one time, so I don't see the utility? It'd just make it harder to read, IMHO.

It's ASCII lexer/parser code, so it's bound to be ugly... :(

Quoted 16 lines

Quoted 5 lines

drivers/net/can/elmcan.c new file +4 -0

+       /* Read CAN ID */
+       if (frame.can_id & CAN_EFF_FLAG) {
+               frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
+                             | (hex_to_bin(elm->rxbuf[1]) << 24)

drivers/net/can/elmcan.c line 490

Quoted 10 lines

drivers/net/can/elmcan.c new file +10 -0

+                             | (hex_to_bin(elm->rxbuf[3]) << 20)
+                             | (hex_to_bin(elm->rxbuf[4]) << 16)
+                             | (hex_to_bin(elm->rxbuf[6]) << 12)
+                             | (hex_to_bin(elm->rxbuf[7]) << 8)
+                             | (hex_to_bin(elm->rxbuf[9]) << 4)
+                             | (hex_to_bin(elm->rxbuf[10]) << 0);
+       } else {
+               frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
+                             | (hex_to_bin(elm->rxbuf[1]) << 4)
+                             | (hex_to_bin(elm->rxbuf[2]) << 0);

Quoted 1 line

hex2bin()?

Good idea!

Quoted 4 lines

drivers/net/can/elmcan.c line 523

Quoted 2 lines

drivers/net/can/elmcan.c new file +2 -0

+       /* Parse the data nibbles. */
+       for (i = 0; i < frame.can_dlc; i++) {

frame.can_dlc is deprecated. Use frame.len instead.

Thanks!

[ ... snip self explanatory stuff ... ]

Quoted 6 lines

Quoted 5 lines

drivers/net/can/elmcan.c new file +4 -0

+       case ELM_RECEIVING:
+               /* Find <CR> delimiting feedback lines. */
+               for (len = 0;
+                    (len < elm->rxfill) && (elm->rxbuf[len] !=

'\r');

Quoted 1 line

Did you use ./script/checkpath?

checkpatch? Yes I did (and kudos to whoever wrote it).

Why?

Quoted 15 lines

drivers/net/can/elmcan.c line 752

Quoted 12 lines

(quoted diff) +2 -0

+/* Dummy needed to use can_rx_offload */
+static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload

*offload,
+ unsigned int n, u32
*timestamp,

drivers/net/can/elmcan.c new file +3 -0

+                                          bool drop)
+{
+       WARN_ON_ONCE(1); /* This function is a dummy, so don't call

it! */ +

drivers/net/can/elmcan.c new file +2 -0

+       return ERR_PTR(-ENOBUFS);
+}

Could you elaborate on why you need can_rx_offload if the mailbox feature is not needed?

The code previously used netif_rx_ni(), and Marc noted that it may reorder packets. To avoid that, he suggested rx_offload:

Message-ID: [email protected]

https://www.spinics.net/lists/linux-can/msg01859.html

But rx_offload needs the mailbox_read function, even if it's a dummy, because can_rx_offload_add_fifo() checks:

        if (!offload->mailbox_read)
                return -EINVAL;

Quoted 12 lines

drivers/net/can/elmcan.c line 837

Quoted 10 lines

drivers/net/can/elmcan.c new file +9 -0

+/* Send a can_frame to a TTY. */
+static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
+                                           struct net_device *dev)
+{
+       struct elmcan *elm = netdev_priv(dev);
+       struct can_frame *frame = (struct can_frame *)skb->data;
+
+       if (skb->len != sizeof(struct can_frame))
+               goto out;

Isn’t this aleardy guaranteed by the upper layers?

Copy-pasta from slcan.c - will look into it.

Quoted 8 lines

drivers/net/can/elmcan.c line 842

Quoted 5 lines

drivers/net/can/elmcan.c new file +4 -0

+       if (!netif_running(dev))  {
+               netdev_warn(elm->dev, "xmit: iface is down.\n");
+               goto out;
+       }

Even if this check succeeds, interface might still go down at the next cycle. What is the purpose of checking if interface is up here?

No purpose. It's copy-pasta from slip.c via slcan.c.

@Vincent - two more things have remained, and I hope it's okay once I explain them:

1. _memstrcmp() - memcmp() vs. str(n)cmp()

The _memstrcmp() function does not compare strings, it compares raw buffers. I am just using C strings for the fixed buffers to compare against, as that allows for shorter and easier to read code. The NUL byte at the end of those strings goes unused.

Also, I have not looked at the assembly produced, since the semantics are different: str(n)cmp() needs to look for NUL bytes in the buffer(s), which is unnecessary here. As a bonus, NUL will never even occur because my code filters those bytes out upon reception from the UART (it's a documented quirk of the ELM327).

Finally, even if I were to use strcmp(), the code would still look just as ugly. Except the machine would also look for NUL bytes, and the next human to read the code would wonder why I'm comparing strings and not buffers.

Hence memcmp(), to help the code self-document and the compiler optimise - I hope that's okay.

Quoted 16 lines · Max Staudt

@Vincent - two more things have remained, and I hope it's okay once I explain them:

1. _memstrcmp() - memcmp() vs. str(n)cmp()

The _memstrcmp() function does not compare strings, it compares raw buffers. I am just using C strings for the fixed buffers to compare against, as that allows for shorter and easier to read code. The NUL byte at the end of those strings goes unused.

Also, I have not looked at the assembly produced, since the semantics are different: str(n)cmp() needs to look for NUL bytes in the buffer(s), which is unnecessary here. As a bonus, NUL will never even occur because my code filters those bytes out upon reception from the UART (it's a documented quirk of the ELM327).

Quoted 7 lines

Finally, even if I were to use strcmp(), the code would still look just as ugly. Except the machine would also look for NUL bytes, and the next human to read the code would wonder why I'm comparing strings and not buffers.

Hence memcmp(), to help the code self-document and the compiler optimise - I hope that's okay.

Looking at the code:

drivers/net/can/elmcan.c line 332

Quoted 4 lines

drivers/net/can/elmcan.c new file +4 -0

+/* Compare a buffer to a fixed string */
+static inline int _memstrcmp(const u8 *mem, const char *str)
+{
+     return memcmp(mem, str, strlen(str));  

The _memstrcmp is sometimes directly used. Where's the check that mem is valid for strlen(len)? Better only use _len_memstrcmp().

Quoted 5 lines

But rx_offload needs the mailbox_read function, even if it's a dummy, because can_rx_offload_add_fifo() checks:

        if (!offload->mailbox_read)
                return -EINVAL;

I think that there should not be a dummy functions like this one.

Either we agree that using can_rx_offload without implementing the mailbox_read() is OK and in that case, the can_rx_offload framework should be modified to allow mailbox_read() to be a NULL pointer.

Either it is not the case and you use the more classic netif_rx().

And I do not have the answer. I haven't studied can_rx_offload enough to be a judge here. Sorry.

@Marc, any thoughts?

Quoted 12 lines

Quoted 11 lines

drivers/net/can/elmcan.c line 837

Quoted 9 lines

drivers/net/can/elmcan.c new file +9 -0

+/* Send a can_frame to a TTY. */
+static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
+                                           struct net_device *dev)
+{
+       struct elmcan *elm = netdev_priv(dev);
+       struct can_frame *frame = (struct can_frame *)skb->data;
+
+       if (skb->len != sizeof(struct can_frame))
+               goto out;

Isn’t this aleardy guaranteed by the upper layers?

Quoted 1 line

Copy-pasta from slcan.c - will look into it.

Also give a look at can_dropped_invalid_skb().

Quoted 8 lines · Vincent Mailhol

Either we agree that using can_rx_offload without implementing the mailbox_read() is OK and in that case, the can_rx_offload framework should be modified to allow mailbox_read() to be a NULL pointer.

Either it is not the case and you use the more classic netif_rx().

Quoted 4 lines

And I do not have the answer. I haven't studied can_rx_offload enough to be a judge here. Sorry.

@Marc, any thoughts?

Use can_rx_offload_add_manual() instead.

Quoted 1 line

Also give a look at can_dropped_invalid_skb().

ACK

Marc

Quoted 12 lines · On Mon, 14 Mar 2022 23:04:08 +0100 Marc Kleine-Budde <[email protected]> wrote:

Quoted 11 lines · Vincent Mailhol

Either we agree that using can_rx_offload without implementing the mailbox_read() is OK and in that case, the can_rx_offload framework should be modified to allow mailbox_read() to be a NULL pointer.

Either it is not the case and you use the more classic netif_rx().

And I do not have the answer. I haven't studied can_rx_offload enough to be a judge here. Sorry.

Quoted 3 lines

Quoted 1 line

@Marc, any thoughts?

Use can_rx_offload_add_manual() instead.

m-(

Yes, it's right underneath _add_fifo() and does the right thing. No idea how I missed it, I thought I had looked through all variants.

Quoted 19 lines · Max Staudt

Quoted 15 lines · On Mon, 14 Mar 2022 23:04:08 +0100 Marc Kleine-Budde <[email protected]> wrote:

Quoted 5 lines · Vincent Mailhol

Either we agree that using can_rx_offload without implementing the mailbox_read() is OK and in that case, the can_rx_offload framework should be modified to allow mailbox_read() to be a NULL pointer.

Quoted 7 lines

Either it is not the case and you use the more classic netif_rx().

And I do not have the answer. I haven't studied can_rx_offload enough to be a judge here. Sorry.

@Marc, any thoughts?

Use can_rx_offload_add_manual() instead.

Quoted 4 lines

m-(

Yes, it's right underneath _add_fifo() and does the right thing. No idea how I missed it, I thought I had looked through all variants.

I think that function was not there form the beginning, maybe you looked at the rx-offload code when it was not available.

drivers/net/can/elmcan.c line 837

Quoted 9 lines

drivers/net/can/elmcan.c new file +9 -0

+/* Send a can_frame to a TTY. */
+static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
+                                           struct net_device *dev)
+{
+       struct elmcan *elm = netdev_priv(dev);
+       struct can_frame *frame = (struct can_frame *)skb->data;
+
+       if (skb->len != sizeof(struct can_frame))
+               goto out;

Isn’t this aleardy guaranteed by the upper layers?

This is the elmcan driver. It does a surprisingly good job at turning ELM327 based OBD-II interfaces into cheap CAN interfaces for simple homebrew projects.

Please see the included documentation for details and limitations:
Documentation/networking/device_drivers/can/elmcan.rst

CC TTY maintainers for their opinion as this patch adds a new ldisc, taking the very last ldisc number available (29) without increasing NR_LDISCS (beyond the current 30).

Cc linux-can <[email protected]>

Cc Greg Kroah-Hartman <[email protected]>

Cc Jiri Slaby <[email protected]>

Signed-off-by Max Staudt <[email protected]>

---
Changes in v3:
- Now depends on c2faf737abfb for new ldisc number 30:

     https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git/commit/?h=tty-next&id=c2faf737abfb10f88f2d2612d573e9edc3c42c37

- Eliminated hardcoded string lengths (GCC will work its magic).
- Emit generic error frames if an error message couldn't be parsed.
- Silence driver startup and init (but still announce ldattach).
- Cleaned up comments, strings, readme.
- Removed sole module option "accept_flaky_uart".
I likely had EMI in earlier testing, which is gone now. This means we can stay strict, unless anyone objects.

Changes in v2:
- Moved to SocketCAN's rx-offload wrapper for NAPI, thus avoiding packets being reordered.
- Updated TTY ldisc code for Linux v5.17-rc3. A lot of cleanup has happened there lately.
- netif_stop_queue() is called earlier in _netdev_close().
- Minor cleanup: More helpful strings and return values.

---
 .../networking/device_drivers/can/elmcan.rst  |  325 +++++
 .../networking/device_drivers/can/index.rst   |    1 +
 MAINTAINERS                                   |    7 +
 drivers/net/can/Kconfig                       |   17 +
 drivers/net/can/Makefile                      |    1 +
 drivers/net/can/elmcan.c                      | 1250 +++++++++++++++++
 include/uapi/linux/tty.h                      |    3 +-
 7 files changed, 1603 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/networking/device_drivers/can/elmcan.rst
 create mode 100644 drivers/net/can/elmcan.c

Documentation/networking/device_drivers/can/elmcan.rst new file +325 -0

new file mode 100644
index 000000000000..7656d62dd58e
@@ -0,0 +1,325 @@
+.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause)
+
+ELM327 driver for Linux SocketCAN
+==================================
+
+Authors
+--------
+
+Max Staudt <[email protected]>
+
+
+
+Motivation
+-----------
+
+This driver aims to lower the initial cost for hackers interested in
+working with CAN buses.
+
+CAN adapters are expensive, few, and far between.
+ELM327 interfaces are cheap and plentiful.
+Let's use ELM327s as CAN adapters.
+
+
+
+Introduction
+-------------
+
+This driver is an effort to turn abundant ELM327 based OBD interfaces
+into full fledged (as far as possible) CAN interfaces.
+
+Since the ELM327 was never meant to be a stand alone CAN controller,
+the driver has to switch between its modes as quickly as possible in
+order to fake full-duplex operation.
+
+As such, elmcan is a best effort driver. However, this is more than
+enough to implement simple request-response protocols (such as OBD II),
+and to monitor broadcast messages on a bus (such as in a vehicle).
+
+Most ELM327s come as nondescript serial devices, attached via USB or
+Bluetooth. The driver cannot recognize them by itself, and as such it
+is up to the user to attach it in form of a TTY line discipline
+(similar to PPP, SLIP, slcan, ...).
+
+This driver is meant for ELM327 versions 1.4b and up, see below for
+known limitations in older controllers and clones.
+
+
+
+Data sheet
+-----------
+
+The official data sheets can be found at ELM electronics' home page:
+
+  https://www.elmelectronics.com/
+
+
+
+How to check the controller version
+------------------------------------
+
+Use a terminal program to attach to the controller.
+The default settings are 38400 baud/s, 8 data bits, no parity, 1 stopbit.
+
+After issuing the "``AT WS``" command, the controller will respond with
+its version::
+
+    >AT WS
+
+
+    ELM327 v1.4b
+
+    >
+
+Note that clones may claim to be any version they like.
+It is not indicative of their actual feature set.
+
+
+
+How to attach the line discipline
+----------------------------------
+
+Every ELM327 chip is factory programmed to operate at a serial setting
+of 38400 baud/s, 8 data bits, no parity, 1 stopbit.
+
+The line discipline can be attached on a command prompt as follows::
+
+    sudo ldattach \
+           --debug \
+           --speed 38400 \
+           --eightbits \
+           --noparity \
+           --onestopbit \
+           --iflag -ICRNL,INLCR,-IXOFF \
+           29 \
+           /dev/ttyUSB0
+
+To change the ELM327's serial settings, please refer to its data
+sheet. This needs to be done before attaching the line discipline.
+
+Once the ldisc is attached, the CAN interface starts out unconfigured.
+Set the speed before starting it:
+
+    # The interface needs to be down to change parameters
+    sudo ip link set can0 down
+    sudo ip link set can0 type can bitrate 500000
+    sudo ip link set can0 up
+
+500000 bit/s is a common rate for OBD-II diagnostics.
+If you're connecting straight to a car's OBD port, this is the speed
+that most cars (but not all!) expect.
+
+After this, you can set out as usual with candump, cansniffer, etc.
+
+
+
+Known limitations of the controller
+------------------------------------
+
+- Clone devices ("v1.5" and others)
+
+  Sending RTR frames is not supported and will be dropped silently.
+
+  Receiving RTR with DLC 8 will appear to be a regular frame with
+  the last received frame's DLC and payload.
+
+  "``AT CSM``" not supported, thus no ACK-ing frames while listening:
+  "``AT MA``" will always be silent. However, immediately after
+  sending a frame, the ELM327 will be in "receive reply" mode, in
+  which it *does* ACK any received frames. Once the bus goes silent
+  or an error occurs (such as BUFFER FULL), the ELM327 will end reply
+  reception mode on its own and elmcan will fall back to "``AT MA``"
+  in order to keep monitoring the bus.
+
+
+- All versions
+
+  No full duplex operation is supported. The driver will switch
+  between input/output mode as quickly as possible.
+
+  The length of outgoing RTR frames cannot be set. In fact, some
+  clones (tested with one identifying as "``v1.5``") are unable to
+  send RTR frames at all.
+
+  We don't have a way to get real-time notifications on CAN errors.
+  While there is a command (``AT CS``) to retrieve some basic stats,
+  we don't poll it as it would force us to interrupt reception mode.
+
+
+- Versions prior to 1.4b
+
+  These versions do not send CAN ACKs when in monitoring mode (AT MA).
+  However, they do send ACKs while waiting for a reply immediately
+  after sending a frame. The driver maximizes this time to make the
+  controller as useful as possible.
+
+  Starting with version 1.4b, the ELM327 supports the "``AT CSM``"
+  command, and the "listen-only" CAN option will take effect.
+
+
+- Versions prior to 1.4
+
+  These chips do not support the "``AT PB``" command, and thus cannot
+  change bitrate or SFF/EFF mode on-the-fly. This will have to be
+  programmed by the user before attaching the line discipline. See the
+  data sheet for details.
+
+
+- Versions prior to 1.3
+
+  These chips cannot be used at all with elmcan. They do not support
+  the "``AT D1``" command, which is necessary to avoid parsing conflicts
+  on incoming data, as well as distinction of RTR frame lengths.
+
+  Specifically, this allows for easy distinction of SFF and EFF
+  frames, and to check whether frames are complete. While it is possible
+  to deduce the type and length from the length of the line the ELM327
+  sends us, this method fails when the ELM327's UART output buffer
+  overruns. It may abort sending in the middle of the line, which will
+  then be mistaken for something else.
+
+
+
+Known limitations of the driver
+--------------------------------
+
+- No 8/7 timing.
+
+  ELM327 can only set CAN bitrates that are of the form 500000/n, where
+  n is an integer divisor.
+  However there is an exception: With a separate flag, it may set the
+  speed to be 8/7 of the speed indicated by the divisor.
+  This mode is not currently implemented.
+
+- No evaluation of command responses.
+
+  The ELM327 will reply with OK when a command is understood, and with ?
+  when it is not. The driver does not currently check this, and simply
+  assumes that the chip understands every command.
+  The driver is built such that functionality degrades gracefully
+  nevertheless. See the section on known limitations of the controller.
+
+- No use of hardware CAN ID filtering
+
+  An ELM327's UART sending buffer will easily overflow on heavy CAN bus
+  load, resulting in the "``BUFFER FULL``" message. Using the hardware
+  filters available through "``AT CF xxx``" and "``AT CM xxx``" would be
+  helpful here, however SocketCAN does not currently provide a facility
+  to make use of such hardware features.
+
+
+
+Communication example
+----------------------
+
+This is a short and incomplete introduction on how to talk to an ELM327.
+
+
+The ELM327 has two modes:
+
+- Command mode
+- Reception mode
+
+In command mode, it expects one command per line, terminated by CR.
+By default, the prompt is a "``>``", after which a command can be
+entered::
+
+    >ATE1
+    OK
+    >
+
+The init script in the driver switches off several configuration options
+that are only meaningful in the original OBD scenario the chip is meant
+for, and are actually a hindrance for elmcan.
+
+
+When a command is not recognized, such as by an older version of the
+ELM327, a question mark is printed as a response instead of OK::
+
+    >ATUNKNOWN
+    ?
+    >
+
+At present, elmcan does not evaluate this response and silently assumes
+that all commands are recognized. It is structured such that it will
+degrade gracefully when a command is unknown. See the sections above on
+known limitations for details.
+
+
+When a CAN frame is to be sent, the target address is configured, after
+which the frame is sent as a command that consists of the data's hex
+dump::
+
+    >ATSH123
+    OK
+    >DEADBEEF12345678
+    OK
+    >
+
+The above interaction sends the frame "``DE AD BE EF 12 34 56 78``" with
+the 11 bit CAN ID ``0x123``.
+For this to function, the controller must be configured for 11 bit CAN
+ID sending mode (using "``AT PB``", see code or datasheet).
+
+
+Once a frame has been sent and wait-for-reply mode is on (``ATR1``,
+configured on ``listen-only=off``), or when the reply timeout expires and
+the driver sets the controller into monitoring mode (``ATMA``), the ELM327
+will send one line for each received CAN frame, consisting of CAN ID,
+DLC, and data::
+
+    123 8 DEADBEEF12345678
+
+For 29 bit CAN frames, the address format is slightly different, which
+elmcan uses to tell the two apart::
+
+    12 34 56 78 8 DEADBEEF12345678
+
+The ELM327 will receive both 11 and 29 bit frames - the current CAN
+config (``ATPB``) does not matter.
+
+
+If the ELM327's internal UART sending buffer runs full, it will abort
+the monitoring mode, print "BUFFER FULL" and drop back into command
+mode. Note that in this case, unlike with other error messages, the
+error message may appear on the same line as the last (usually
+incomplete) data frame::
+
+    12 34 56 78 8 DEADBEEF123 BUFFER FULL
+
+
+
+Rationale behind the chosen configuration
+------------------------------------------
+
+``AT E1``
+  Echo on
+
+  We need this to be able to get a prompt reliably.
+
+``AT S1``
+  Spaces on
+
+  We need this to distinguish 11/29 bit CAN addresses received.
+
+  Note:
+  We can usually do this using the line length (odd/even),
+  but this fails if the line is not transmitted fully to
+  the host (BUFFER FULL).
+
+``AT D1``
+  DLC on
+
+  We need this to tell the "length" of RTR frames.
+
+
+
+A note on CAN bus termination
+------------------------------
+
+Your adapter may have resistors soldered in which are meant to terminate
+the bus. This is correct when it is plugged into a OBD-II socket, but
+not helpful when trying to tap into the middle of an existing CAN bus.
+
+If communications don't work with the adapter connected, check for the
+termination resistors on its PCB and try removing them.

Documentation/networking/device_drivers/can/index.rst +1 -0

index 58b6e0ad3030..e3f2be735aef 100644
@@ -10,6 +10,7 @@ Contents:
 .. toctree::
    :maxdepth: 2
 
+   elmcan
    freescale/flexcan
 
 .. only::  subproject and html

MAINTAINERS +7 -0

index 3e461db9cd91..7bb266dbffd1 100644
@@ -7064,6 +7064,13 @@ L:	[email protected]
 S:	Maintained
 F:	drivers/net/ethernet/ibm/ehea/
 
+ELM327 CAN NETWORK DRIVER
+M:	Max Staudt <[email protected]>
+L:	[email protected]
+S:	Maintained
+F:	Documentation/networking/device_drivers/can/elmcan.rst
+F:	drivers/net/can/elmcan.c
+
 EM28XX VIDEO4LINUX DRIVER
 M:	Mauro Carvalho Chehab <[email protected]>
 L:	[email protected]

drivers/net/can/Kconfig +17 -0

index fff259247d52..226bd00fc048 100644
@@ -180,6 +180,23 @@ source "drivers/net/can/softing/Kconfig"
 source "drivers/net/can/spi/Kconfig"
 source "drivers/net/can/usb/Kconfig"
 
+config CAN_ELMCAN
+	tristate "Serial / USB serial ELM327 based OBD-II Interfaces (elmcan)"
+	depends on TTY
+	help
+	  CAN driver for several 'low cost' OBD-II interfaces based on the
+	  ELM327 OBD-II interpreter chip.
+
+	  This is a best effort driver - the ELM327 interface was never
+	  designed to be used as a standalone CAN interface. However, it can
+	  still be used for simple request-response protocols (such as OBD II),
+	  and to monitor broadcast messages on a bus (such as in a vehicle).
+
+	  Please refer to the documentation for information on how to use it:
+	  Documentation/networking/device_drivers/can/elmcan.rst
+
+	  If this driver is built as a module, it will be called elmcan.
+
 endif
 
 config CAN_DEBUG_DEVICES

drivers/net/can/Makefile +0 -0

index 1e660afcb61b..c25a0f8a397b 100644

drivers/net/can/Makefile +0 -0

 obj-y				+= dev/
 obj-y				+= rcar/

drivers/net/can/elmcan.c new file +0 -0

new file mode 100644
index 000000000000..2d7ebc40a492

drivers/net/can/elmcan.c new file +23 -0

+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/ctype.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/if_ether.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/tty.h>
+#include <linux/tty_ldisc.h>
+#include <linux/workqueue.h>
+
+#include <uapi/linux/tty.h>
+

drivers/net/can/elmcan.c new file +7 -0

+
+#define ELM327_NAPI_WEIGHT 4
+
+#define ELM327_SIZE_RXBUF 256
+#define ELM327_SIZE_TXBUF 32
+
+#define ELM327_CAN_CONFIG_SEND_SFF           0x8000

drivers/net/can/elmcan.c new file +4 -0

+	TODO_CAN_DATA = 0,
+	TODO_CANID_11BIT,
+	TODO_CANID_29BIT_LOW,
+	TODO_CANID_29BIT_HIGH,

drivers/net/can/elmcan.c new file +30 -0

+
+	struct can_rx_offload offload;
+
+	/* TTY and netdev devices that we're bridging */
+	struct tty_struct	*tty;
+	struct net_device	*dev;
+
+	/* Per-channel lock */
+	spinlock_t		lock;
+
+	/* Keep track of how many things are using this struct.
+	 * Once it reaches 0, we are in the process of cleaning up,
+	 * and new operations will be cancelled immediately.
+	 * Use atomic_t rather than refcount_t because we deliberately
+	 * decrement to 0, and refcount_dec() spills a WARN_ONCE in
+	 * that case.
+	 */
+	atomic_t		refcount;
+
+	/* Stop the channel on hardware failure.
+	 * Once this is true, nothing will be sent to the TTY.
+	 */
+	bool			hw_failure;
+
+	/* TTY TX helpers */
+	struct work_struct	tx_work;	/* Flushes TTY TX buffer   */
+	unsigned char		*txbuf;
+	unsigned char		*txhead;	/* Pointer to next TX byte */
+	int			txleft;		/* Bytes left to TX */
+

drivers/net/can/elmcan.c new file +6 -0

+
+	/* Things we have yet to send */
+	char **next_init_cmd;
+	unsigned long cmds_todo;
+};
+

drivers/net/can/elmcan.c new file +43 -0

+	if (elm->hw_failure)
+		return;
+
+	memcpy(elm->txbuf, buf, len);
+
+	/* Order of next two lines is *very* important.
+	 * When we are sending a little amount of data,
+	 * the transfer may be completed inside the ops->write()
+	 * routine, because it's running with interrupts enabled.
+	 * In this case we *never* got WRITE_WAKEUP event,
+	 * if we did not request it before write operation.
+	 *       14 Oct 1994  Dmitry Gorodchanin.
+	 */
+	set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
+	actual = elm->tty->ops->write(elm->tty, elm->txbuf, len);
+	if (actual < 0) {
+		netdev_err(elm->dev,
+			   "Failed to write to tty %s.\n",
+			   elm->tty->name);
+		elm327_hw_failure(elm);
+		return;
+	}
+
+	elm->txleft = len - actual;
+	elm->txhead = elm->txbuf + actual;
+}
+
+/* Take the ELM327 out of almost any state and back into command mode.
+ * We send ELM327_DUMMY_CHAR which will either abort any running
+ * operation, or be echoed back to us in case we're already in command
+ * mode.
+ *
+ * Assumes elm->lock taken.
+ */
+static void elm327_kick_into_cmd_mode(struct elmcan *elm)
+{
+	if (elm->state != ELM_GETDUMMYCHAR && elm->state != ELM_GETPROMPT) {
+		elm327_send(elm, ELM327_DUMMY_STRING, 1);
+
+		elm->state = ELM_GETDUMMYCHAR;
+	}
+}
+

drivers/net/can/elmcan.c new file +208 -0

+		    ^ (elm->can_frame.can_id & CAN_EFF_FLAG)) {
+			elm->can_config = (frame->can_id & CAN_EFF_FLAG
+						? 0
+						: ELM327_CAN_CONFIG_SEND_SFF)
+					| ELM327_CAN_CONFIG_VARIABLE_DLC
+					| ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
+					| elm->can_bitrate_divisor;
+
+			set_bit(TODO_CAN_CONFIG, &elm->cmds_todo);
+		}
+
+		if (frame->can_id & CAN_EFF_FLAG) {
+			clear_bit(TODO_CANID_11BIT, &elm->cmds_todo);
+			set_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo);
+			set_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo);
+		} else {
+			set_bit(TODO_CANID_11BIT, &elm->cmds_todo);
+			clear_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo);
+			clear_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo);
+		}
+	}
+
+	/* Schedule the CAN frame itself. */
+	elm->can_frame = *frame;
+	set_bit(TODO_CAN_DATA, &elm->cmds_todo);
+
+	elm327_kick_into_cmd_mode(elm);
+}
+
+/* ELM327 initialization sequence.
+ *
+ * Assumes elm->lock taken.
+ */
+static char *elm327_init_script[] = {
+	"AT WS\r",        /* v1.0: Warm Start */
+	"AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
+	"AT M0\r",        /* v1.0: Memory Off */
+	"AT AL\r",        /* v1.0: Allow Long messages */
+	"AT BI\r",        /* v1.0: Bypass Initialization */
+	"AT CAF0\r",      /* v1.0: CAN Auto Formatting Off */
+	"AT CFC0\r",      /* v1.0: CAN Flow Control Off */
+	"AT CF 000\r",    /* v1.0: Reset CAN ID Filter */
+	"AT CM 000\r",    /* v1.0: Reset CAN ID Mask */
+	"AT E1\r",        /* v1.0: Echo On */
+	"AT H1\r",        /* v1.0: Headers On */
+	"AT L0\r",        /* v1.0: Linefeeds Off */
+	"AT SH 7DF\r",    /* v1.0: Set CAN sending ID to 0x7df */
+	"AT ST FF\r",     /* v1.0: Set maximum Timeout for response after TX */
+	"AT AT0\r",       /* v1.2: Adaptive Timing Off */
+	"AT D1\r",        /* v1.3: Print DLC On */
+	"AT S1\r",        /* v1.3: Spaces On */
+	"AT TP B\r",      /* v1.0: Try Protocol B */
+	NULL
+};
+
+static void elm327_init(struct elmcan *elm)
+{
+	elm->state = ELM_NOTINIT;
+	elm->can_frame.can_id = 0x7df;
+	elm->rxfill = 0;
+	elm->drop_next_line = 0;
+
+	/* We can only set the bitrate as a fraction of 500000.
+	 * The bit timing constants in elmcan_bittiming_const will
+	 * limit the user to the right values.
+	 */
+	elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
+	elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
+			| ELM327_CAN_CONFIG_VARIABLE_DLC
+			| ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
+			| elm->can_bitrate_divisor;
+
+	/* Configure ELM327 and then start monitoring */
+	elm->next_init_cmd = &elm327_init_script[0];
+	set_bit(TODO_INIT, &elm->cmds_todo);
+	set_bit(TODO_SILENT_MONITOR, &elm->cmds_todo);
+	set_bit(TODO_RESPONSES, &elm->cmds_todo);
+	set_bit(TODO_CAN_CONFIG, &elm->cmds_todo);
+
+	elm327_kick_into_cmd_mode(elm);
+}
+
+/* Assumes elm->lock taken. */
+static void elm327_feed_frame_to_netdev(struct elmcan *elm,
+					const struct can_frame *frame)
+{
+	struct can_frame *cf;
+	struct sk_buff *skb;
+
+	if (!netif_running(elm->dev))
+		return;
+
+	skb = alloc_can_skb(elm->dev, &cf);
+
+	if (!skb)
+		return;
+
+	memcpy(cf, frame, sizeof(struct can_frame));
+
+	/* Queue for NAPI pickup.
+	 * rx-offload will update stats and LEDs for us.
+	 */
+	if (can_rx_offload_queue_tail(&elm->offload, skb))
+		elm->dev->stats.rx_fifo_errors++;
+
+	/* Wake NAPI */
+	can_rx_offload_irq_finish(&elm->offload);
+}
+
+/* Called when we're out of ideas and just want it all to end.
+ * Assumes elm->lock taken.
+ */
+static inline void elm327_hw_failure(struct elmcan *elm)
+{
+	struct can_frame frame;
+
+	memset(&frame, 0, sizeof(frame));
+	frame.can_id = CAN_ERR_FLAG;
+	frame.can_dlc = CAN_ERR_DLC;
+	frame.data[5] = 'R';
+	frame.data[6] = 'I';
+	frame.data[7] = 'P';
+	elm327_feed_frame_to_netdev(elm, &frame);
+
+	netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
+
+	elm->hw_failure = true;
+	can_bus_off(elm->dev);
+}
+
+/* Compare a buffer to a fixed string */
+static inline int _memstrcmp(const u8 *mem, const char *str)
+{
+	return memcmp(mem, str, strlen(str));
+}
+
+/* Compare buffer to string length, then compare buffer to fixed string.
+ * This ensures two things:
+ *  - It flags cases where the fixed string is only the start of the
+ *    buffer, rather than exactly all of it.
+ *  - It avoids byte comparisons in case the length doesn't match.
+ */
+static inline int _len_memstrcmp(const u8 *mem, size_t mem_len, const char *str)
+{
+	size_t str_len = strlen(str);
+
+	return (mem_len != str_len) || memcmp(mem, str, str_len);
+}
+
+/* Assumes elm->lock taken. */
+static void elm327_parse_error(struct elmcan *elm, size_t len)
+{
+	struct can_frame frame;
+
+	memset(&frame, 0, sizeof(frame));
+	frame.can_id = CAN_ERR_FLAG;
+	frame.can_dlc = CAN_ERR_DLC;
+
+	/* Filter possible error messages based on length of RX'd line */
+	if (!_len_memstrcmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
+		netdev_err(elm->dev,
+			   "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
+	} else if (!_len_memstrcmp(elm->rxbuf, len, "BUFFER FULL")) {
+		/* This will only happen if the last data line was complete.
+		 * Otherwise, elm327_parse_frame() will heuristically
+		 * emit this kind of error frame instead.
+		 */
+		frame.can_id |= CAN_ERR_CRTL;
+		frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
+	} else if (!_len_memstrcmp(elm->rxbuf, len, "BUS ERROR")) {
+		frame.can_id |= CAN_ERR_BUSERROR;
+	} else if (!_len_memstrcmp(elm->rxbuf, len, "CAN ERROR")) {
+		frame.can_id |= CAN_ERR_PROT;
+	} else if (!_len_memstrcmp(elm->rxbuf, len, "<RX ERROR")) {
+		frame.can_id |= CAN_ERR_PROT;
+	} else if (!_len_memstrcmp(elm->rxbuf, len, "BUS BUSY")) {
+		frame.can_id |= CAN_ERR_PROT;
+		frame.data[2] = CAN_ERR_PROT_OVERLOAD;
+	} else if (!_len_memstrcmp(elm->rxbuf, len, "FB ERROR")) {
+		frame.can_id |= CAN_ERR_PROT;
+		frame.data[2] = CAN_ERR_PROT_TX;
+	} else if (len == 5 && !_memstrcmp(elm->rxbuf, "ERR")) {
+		/* ERR is followed by two digits, hence line length 5 */
+		netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
+			   elm->rxbuf[3], elm->rxbuf[4]);
+		frame.can_id |= CAN_ERR_CRTL;
+	} else {
+		/* Something else has happened.
+		 * Maybe garbage on the UART line.
+		 * Emit a generic error frame.
+		 */
+	}
+
+	elm327_feed_frame_to_netdev(elm, &frame);
+}
+
+/* Parse CAN frames coming as ASCII from ELM327.
+ * They can be of various formats:
+ *
+ * 29-bit ID (EFF):  12 34 56 78 D PL PL PL PL PL PL PL PL
+ * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
+ *
+ * where D = DLC, PL = payload byte
+ *
+ * Instead of a payload, RTR indicates a remote request.
+ *
+ * We will use the spaces and line length to guess the format.
+ *

drivers/net/can/elmcan.c new file +28 -0

+
+	/* Find first non-hex and non-space character:
+	 *  - In the simplest case, there is none.
+	 *  - For RTR frames, 'R' is the first non-hex character.
+	 *  - An error message may replace the end of the data line.
+	 */
+	for (hexlen = 0; hexlen <= len; hexlen++) {
+		if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
+		    elm->rxbuf[hexlen] != ' ') {
+			break;
+		}
+	}
+
+	/* Sanity check whether the line is really a clean hexdump,
+	 * or terminated by an error message, or contains garbage.
+	 */
+	if (hexlen < len &&
+	    !isdigit(elm->rxbuf[hexlen]) &&
+	    !isupper(elm->rxbuf[hexlen]) &&
+	    '<' != elm->rxbuf[hexlen] &&
+	    ' ' != elm->rxbuf[hexlen]) {
+		/* The line is likely garbled anyway, so bail.
+		 * The main code will restart listening.
+		 */
+		return -ENODATA;
+	}
+
+	/* Use spaces in CAN ID to distinguish 29 or 11 bit address length.

drivers/net/can/elmcan.c new file +27 -0

+		datastart = 6;
+	} else {
+		/* This is not a well-formatted data line.
+		 * Assume it's an error message.
+		 */
+		return -ENODATA;
+	}
+
+	if (hexlen < datastart) {
+		/* The line is too short to be a valid frame hex dump.
+		 * Something interrupted the hex dump or it is invalid.
+		 */
+		return -ENODATA;
+	}
+
+	/* From here on all chars up to buf[hexlen] are hex or spaces,
+	 * at well-defined offsets.
+	 */
+
+	/* Read CAN data length */
+	frame.can_dlc = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
+
+	/* Read CAN ID */
+	if (frame.can_id & CAN_EFF_FLAG) {
+		frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
+			      | (hex_to_bin(elm->rxbuf[1]) << 24)
+			      | (hex_to_bin(elm->rxbuf[3]) << 20)

drivers/net/can/elmcan.c new file +24 -0

+
+	/* Check for RTR frame */
+	if (elm->rxfill >= hexlen + 3 &&
+	    !_memstrcmp(&elm->rxbuf[hexlen], "RTR")) {
+		frame.can_id |= CAN_RTR_FLAG;
+	}
+
+	/* Is the line long enough to hold the advertised payload?
+	 * Note: RTR frames have a DLC, but no actual payload.
+	 */
+	if (!(frame.can_id & CAN_RTR_FLAG) &&
+	    (hexlen < frame.can_dlc * 3 + datastart)) {
+		/* Incomplete frame. */
+
+		/* Probably the ELM327's RS232 TX buffer was full.
+		 * Emit an error frame and exit.
+		 */
+		frame.can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
+		frame.can_dlc = CAN_ERR_DLC;
+		frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
+		elm327_feed_frame_to_netdev(elm, &frame);
+
+		/* Signal failure to parse.
+		 * The line will be re-parsed as an error line, which will fail.