Add Loongson CAN-FD controller driver

Hi all:

This patchset adds support for the CAN-FD controller found on Loongson CPUs.

Patch 1 introduces the basic CAN-FD controller driver with support for classic CAN and CAN FD, including bit timing, error handling, NAPI-based RX, and multiple TX buffers.

Patch 2 adds optional DMA support for RX path using the Loongson APB CMC DMA engine, which significantly reduces CPU load under high receive throughput.

The driver has been tested on Loongson-2K3000 platforms with various CAN/CAN FD traffic patterns.

Finally, I'd like to thank Bingxiong, the original author of this driver, for his efforts in working on the patch.

Thanks.
Binbin

=========
V7:
Patch (1/2):
- Fix can_bittiming_const->tseg1_max;
- Fix TX buffer id in loongson_canfd_start_xmit();
- Add rwcnt checking in loongson_canfd_rx()
- Add netdev stats spinlock;
- Add net_ratelimit() to control log output in loongson_canfd_err_interrupt);
- Rewrite loongson_canfd_rx_napi() to clearly distinguish between the two scenarios: "no more data to process" and "quota exhausted".

Patch (2/2):
- Put dmaengine_terminate_sync() before loongson_canfd_rxdma_free();

Link to V6:
https://lore.kernel.org/all/[email protected]/

V6:
- Rebase on linux-can/master;
Patch (1/2):
- Drop CAN_CTRLMODE_3_SAMPLES ctrlmode;
- Replace kfree_skb() with dev_kfree_skb_any();
- Drop REG_CMD_ERCRST operation;
- Rewrite loongson_canfd_tx_interrupt() to prevent duplicate handling of TX completion';
Patch (2/2):
- Added a fallback to true when dmaengine_tx_status() returns an error;
- Replaced all direct regmap_read() from LOONGSON_CANFD_RX_DATA with the priv->get_rx_data() callback;
- Release the DMA channel and clear priv->rx_ch on dma_alloc_coherent() failure;

Link to V5:
https://lore.kernel.org/all/[email protected]/

V5:
Patch (1/2):
- Fix tseg1_max const value;
- Empty FIFO when SKB allocate failed.
- Use REG_FRAME_META1_RWCNT as the playload read count value;
- Only clean processed interrupt flags in loongson_canfd_err_interrupt();
- Refact loongson_canfd_tx_interrupt();
- Add LOONGSON_CANFD_TRV_DLY into loongson_canfd_volatile_reg();
Patch (2/2):
- Fix dma_request_chan() error path;
- Fix build error;
- Fix loongson_canfd_rxdma_init() error path;

Link to V4:
https://lore.kernel.org/all/[email protected]/

V4:
- Fix some issues from sashiko.
Patch (1/2):
- Update commit message;
- Use common APIs to calculate DLC;
- Correct CAN_RTR_FLAG judgement;
- Add skb check for CAN_STATE_ERROR_ACTIVE case;
- Use regmap_write() rather than regmap_update_bits() to disable all interrupts;
- Add napi_disable() in error paths;
- Add clock-frequency return value check;
- More comments for macros.

Link to V3:
https://lore.kernel.org/all/[email protected]/

V3:
Patch (1/2):
- Replace the switch-case statement with a calculated mask in loongson_canfd_get_txbuf_sts();
- Change loongson_canfd_reset() return type to void;
- Drop old code in loongson_canfd_set_btr();
- Rename loongson_canfd_set_mode() to loongson_canfd_set_conf_mode();
- Drop cf->__res* usage;
- Drop unnecessary macro definitions;
- Add netif_napi_del() in probe error route path;
- Replace ternary operator with if-else;
- Drop stats->rx_packets and stats->rx_bytes count in CAN error frames;
- Add ethtool_ops;
- Add CAN_CTRLMODE_CC_LEN8_DLC;

Patch (2/2):
- Fix W=2 warning;
- Rename get_rx_frc() -> get_rxbuf_empty();
- Put loongson_canfd_rxdma_remove() before free_candev();
- Adjust the RXDMA probe process.

Link to V2:
https://lore.kernel.org/all/[email protected]/

V2:
Patch (1/2):
- Put all code into one file;
- Add COMPILE_TEST Kconfig option;
- Rewrite Kconfig description;
- Use regmap_test_bits() to simplify bit field checks;
- Drop odd FIELD_GET() usage;
- Don't use FIELD_GET() for a single bit;
- Use an if/else instead of the ternary operator;
- Use the CAN TDC framework to get the SSP value;
- Use guard(spinlock)/scoped_guard(spinlock);
- Use netdev_debug() to be less verboss;
- Check for memory allocation failure;
- Add CAN_ERR_CNT flag;
- Drop unused REG_DATA_xx_yy_W_DATA_yy definition;
- Add more function comment;

Link to V1:
https://lore.kernel.org/all/[email protected]/

Binbin Zhou (2):
can: Add Loongson CAN-FD controller driver
can: loongson_canfd: Add RXDMA support

 MAINTAINERS                      |    7 +
 drivers/net/can/Kconfig          |   11 +
 drivers/net/can/Makefile         |    1 +
 drivers/net/can/loongson_canfd.c | 1913 ++++++++++++++++++++++++++++++
 4 files changed, 1932 insertions(+)
 create mode 100644 drivers/net/can/loongson_canfd.c

base-commit: 3bd438a58e910db5dc369aa25dfed1fc95f1b596

2.52.0

Add a new driver for the Loongson CAN-FD controller, which is integrated into Loongson-2K series SoCs. The controller supports both CAN 2.0 and CAN-FD protocols, with up to 8 TX buffers and a flexible RX buffer.

The driver implements the core CAN device operations:
- NAPI-based receive path with interrupt masking to reduce overhead;
- TX echo support for accurate loopback and echo skb handling;
- Error reporting (warning, passive, bus-off) with detailed status;
- Support for common CAN controller modes: loopback, listen-only, one-shot, FD, and non-ISO FD;
- Auto TDC (Transmitter Delay Compensation) for FD data phase.

---
 MAINTAINERS                      |    7 +
 drivers/net/can/Kconfig          |   11 +
 drivers/net/can/Makefile         |    1 +
 drivers/net/can/loongson_canfd.c | 1722 ++++++++++++++++++++++++++++++
 4 files changed, 1741 insertions(+)
 create mode 100644 drivers/net/can/loongson_canfd.c

index 61126d170e4a..5a27643eb161 100644
@@ -15195,6 +15195,13 @@ F:	Documentation/devicetree/bindings/sound/loongson,ls2k1000-i2s.yaml
 F:	sound/soc/loongson/loongson_*.c
 F:	sound/soc/loongson/loongson_*.h
 
+LOONGSON CAN FD DRIVER
+M:	Bingxiong Li <[email protected]>
+M:	Binbin Zhou <[email protected]>
+L:	[email protected]
+S:	Maintained
+F:	drivers/net/can/loongson_canfd/
+
 LOONGSON GPIO DRIVER
 M:	Yinbo Zhu <[email protected]>
 L:	[email protected]

index a8fad6fe5302..95a0f898959c 100644
@@ -186,6 +186,17 @@ config CAN_KVASER_PCIEFD
 	    Kvaser M.2 PCIe 4xCAN
 	    Kvaser PCIe 8xCAN
 
+config CAN_LOONGSON_CANFD
+	tristate "Loongson CAN-FD controller"
+	depends on HAS_IOMEM
+	select REGMAP_MMIO
+	help
+	  This is a canfd driver switch for the Loongson platform,
+	  integrated with the Loongson-2K series SoCs.
+
+	  To compile as a module, choose M here: the module will be
+	  called loongson_canfd.
+
 config CAN_SLCAN
 	tristate "Serial / USB serial CAN Adaptors (slcan)"
 	depends on TTY

index 4010d17f8583..c4eae4595ce3 100644
@@ -27,6 +27,7 @@ obj-$(CONFIG_CAN_GRCAN)		+= grcan.o
 obj-$(CONFIG_CAN_IFI_CANFD)	+= ifi_canfd/
 obj-$(CONFIG_CAN_JANZ_ICAN3)	+= janz-ican3.o
 obj-$(CONFIG_CAN_KVASER_PCIEFD)	+= kvaser_pciefd/
+obj-$(CONFIG_CAN_LOONGSON_CANFD)	+= loongson_canfd.o
 obj-$(CONFIG_CAN_MSCAN)		+= mscan/
 obj-$(CONFIG_CAN_M_CAN)		+= m_can/
 obj-$(CONFIG_CAN_PEAK_PCIEFD)	+= peak_canfd/

2.52.0

Extend the driver with an optional DMA engine support for the receive path. When a DMA channel named rx is available (e.g., from the loongson2-apb-cmc-dma driver), the RX buffer is mapped to a cyclic DMA transfer that continuously fills a pre-allocated ring buffer. The driver then readds incoming CAN frames directly from the DMA buffer, reducing the number of MMIO accesses and improving performance under high traffic.

The DMA mode is completely transparent to the under networking stack; the driver automatically selects the appropriate RX data reading method based on the availability of the DMA channel.

---
 drivers/net/can/Kconfig          |   2 +-
 drivers/net/can/loongson_canfd.c | 231 ++++++++++++++++++++++++++++---
 2 files changed, 212 insertions(+), 21 deletions(-)

index 95a0f898959c..07a51aed54d0 100644
@@ -188,7 +188,7 @@ config CAN_KVASER_PCIEFD
 
 config CAN_LOONGSON_CANFD
 	tristate "Loongson CAN-FD controller"
-	depends on HAS_IOMEM
+	depends on HAS_IOMEM && (LOONGSON2_APB_CMC_DMA || COMPILE_TEST)
 	select REGMAP_MMIO
 	help
 	  This is a canfd driver switch for the Loongson platform,

2.52.0