can: virtio: Add virtio CAN driver

Add virtio CAN driver based on Virtio 1.4 specification (see
https://github.com/oasis-tcs/virtio-spec/tree/virtio-1.4). The driver implements a complete CAN bus interface over Virtio transport, supporting both CAN Classic and CAN-FD Ids. In term of frames, it supports classic and CAN FD. RTR frames are only supported with classic CAN.

Usage:
- "ip link set up can0" - start controller
- "ip link set down can0" - stop controller
- "candump can0" - receive frames
- "cansend can0 123#DEADBEEF" - send frames

---
V14:
- set length before memcpy() for field defined with __counted_by_le()
- move napi_enable() to open() and napi_disable() to close() thus following pattern in other CAN devices
- add flag to prevent remove() to hang if restore() fails

V13:
- kick device only when some buffers have been added
- add virtio_can_del_vq() when virtio_can_start() fails
- move napi_disable() at the end of virtio_can_freeze()
- move napi_enable() at beginning of virtio_can_restore()
- let virtio_can_start() sets CAN_STATE_ERROR_ACTIVE
- in freeze(), if can_stop() fails, restore the state of the device
- in restore(), if !netif_running, set CAN_STATE_STOPPED

V12:
- check return value in virtio_can_start()
- use devm_krealloc() in virtio_can_restore() to re-allocate rpkt
- remove access to cf->len and replace it with len
- use __counted_by_le()
- free tx buffers during virtio_can_del_vq()
- add reinit_completion() for ctrl msgs

V11:
* Set CAN_VIRTIO_CAN config before CAN_XILINXCAN
* Use GFP_ATOMIC in virtio_can_alloc_tx_idx()
* Use open_candev() and set bittiming.bitrate to CAN_BITRATE_UNKNOWN and data_bittiming.bitrate to CAN_BITRATE_UNKNOWN
* Fix leak of skb by adding kfree_skb(skb)
* Fix out-of-bounds in virtio_can_populate_rx_vq()
* Initialize ret
* Use virtio_reset_device()
* Add napi_disable() in virtio_can_remove()
* Propagate error in virtio_can_start() and virtio_can_stop()

V10:
* Follow Reverse Christmas Tree convention

V9:
* Remove unnecessary comments
* Update maintainer list

V8:
* Address nits

V7:
* Address nits
* Remove unnecessary comments
* Remove io_callbacks[]
* Use guard() syntax
* Remove kicking for each inbuf
* replace sdu_len with rpkt_len
* Use devm_kzalloc()
* Use scoped_guard() to protect virtqueue_add_sgs() and virtqueue_kicks() for tx queue
* Tested with vhost-device-can
(see https://github.com/rust-vmm/vhost-device/tree/main/vhost-device-can) and Qemu (942b0d3) with [1]. A reviewer observed that the device stops to work after flooding from host. This issue is still present.

[1]
https://lore.kernel.org/qemu-devel/[email protected]/

V6:
* Address nits
* Check for error during register_virtio_can()
* Remove virtio_device_ready()
* Allocate virtio_can_rx rpkt[] at probe
* Define virtio_can_control struct
* Return VIRTIO_CAN_RESULT_NOT_OK after unlocking
* Define sdu[] as a flex array for both tx and rx. For rx, use VIRTIO_CAN_F_CAN_FD to figure out the max len for sdu
* Fix statistics in virtio_can_read_tx_queue() and
how we indicate error to the user when getting VIRTIO_CAN_RESULT_NOT_OK
* Fix syntax of virtio_find_vqs()
* Drop tx_list
* Fix values of VIRTIO_CAN_F_LATE_TX_ACK and VIRTIO_CAN_F_RTR_FRAMES
* Tested with vhost-device-can
(see
https://github.com/rust-vmm/vhost-device/tree/main/vhost-device-can)
and qemu (see
https://github.com/virtualopensystems/qemu/tree/vhu-can-rfc)

V5:
* Re-base on top of linux-next (next-20240103)
* Tested with https://github.com/OpenSynergy/qemu/tree/virtio-can-spec-rfc-v3

RFC V4:
* Apply reverse Christmas tree style
* Add member *classic_dlc to RX and TX CAN frames
* Fix race causing a NETDEV_TX_BUSY return

---
 MAINTAINERS                     |    9 +
 drivers/net/can/Kconfig         |   12 +
 drivers/net/can/Makefile        |    1 +
 drivers/net/can/virtio_can.c    | 1007 +++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_can.h |   78 +++
 5 files changed, 1107 insertions(+)
 create mode 100644 drivers/net/can/virtio_can.c
 create mode 100644 include/uapi/linux/virtio_can.h

index 80cd3498c293..f295a904c93e 100644
@@ -27068,6 +27068,15 @@ F:	drivers/scsi/virtio_scsi.c
 F:	include/uapi/linux/virtio_blk.h
 F:	include/uapi/linux/virtio_scsi.h
 
+VIRTIO CAN DRIVER
+M:	"Harald Mommer" <[email protected]>
+M:	"Matias Ezequiel Vara Larsen" <[email protected]>
+L:	[email protected]
+L:	[email protected]
+S:	Maintained
+F:	drivers/net/can/virtio_can.c
+F:	include/uapi/linux/virtio_can.h
+
 VIRTIO CONSOLE DRIVER
 M:	Amit Shah <[email protected]>
 L:	[email protected]

index d43d56694667..f33ae46d9766 100644
@@ -209,6 +209,18 @@ config CAN_TI_HECC
 	  Driver for TI HECC (High End CAN Controller) module found on many
 	  TI devices. The device specifications are available from www.ti.com
 
+config CAN_VIRTIO_CAN
+	depends on VIRTIO
+	tristate "Virtio CAN device support"
+	default n
+	help
+	  Say Y here if you want to support for Virtio CAN.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called virtio-can.
+
+	  If unsure, say N.
+
 config CAN_XILINXCAN
 	tristate "Xilinx CAN"
 	depends on ARCH_ZYNQ || ARM64 || MICROBLAZE || COMPILE_TEST

index 56138d8ddfd2..2ddea733ed5d 100644
@@ -32,6 +32,7 @@ obj-$(CONFIG_CAN_PEAK_PCIEFD)	+= peak_canfd/
 obj-$(CONFIG_CAN_SJA1000)	+= sja1000/
 obj-$(CONFIG_CAN_SUN4I)		+= sun4i_can.o
 obj-$(CONFIG_CAN_TI_HECC)	+= ti_hecc.o
+obj-$(CONFIG_CAN_VIRTIO_CAN)	+= virtio_can.o
 obj-$(CONFIG_CAN_XILINXCAN)	+= xilinx_can.o
 
 subdir-ccflags-$(CONFIG_CAN_DEBUG_DEVICES) += -DDEBUG

2.42.0