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

=========
V9:
Patch (1/2):
- Add hardware timestamping support;
- Refactor RX into descriptor parsing/validation/delivery;
- Improve IRQ handling: add DOI overrun handlinga;
- Improve TX path: add free TX buffer helper, support CC_LEN8_DLC;
- Split error reporting into state-change/arb-loss/bus-error helpers;
- Cancel restart_work before free_irq();
Patch (2/2):
- Enlarge RX DMA ring to 32K and use 4K cyclic DMA periods.
- Split DMA init from start/stop; start DMA before chip_start(), stop after chip_stop(), and restart DMA on CAN_MODE_START.
- Add DMA RX empty/overrun/bad-header recovery, partial-header -EAGAIN retry with bounded cpu_relax(), and pointer resync.
- Rename RX callbacks to read_rx_word/rx_is_empty/process_rx;
- Release DMA on probe/register error and in remove().

Testing & Validation:
----------------------
To validate the robustness and data integrity of this driver patch, extensive stress tests were conducted across two different speed configurations under high bus load.

To prove both system stability and data correctness, the test suite introduced strict data integrity checks at the payload level:

1. Traffic Generation & Load Control:
- Traffic consists of both periodic business PDUs (20ms, 50ms, 100ms, 200ms) and 64-byte fill frames.
- An accumulator-based algorithm is used to precisely maintain an 80% total bus load on both ends without bursting the driver queues.

2. Data Integrity Verification:
- Each frame payload embeds a 32-bit sequence number (SEQ32), a deterministic data fingerprint, and a CRC32 checksum.
- The receiving ends strictly verify every received frame (including fill frames) against these metrics to detect any bit flips, payload corruption, or frame duplication.

3. Test Case A: 500 kbps / 2 Mbps (Industry Baseline)
- Duration: ~66 hours.
- Throughput: Over 20 million business frames and 160 million fill frames.
- Results: 0 CRC errors, 0 fingerprint mismatches, and 0 duplicated frames. The overall frame loss rate was 0.00%. The driver handled transient bus interference gracefully (2 "error-warn" events) without any Bus-Off.

4. Test Case B: 1 Mbps / 4 Mbps (High-Speed Stress)
- Duration: ~45.5 hours.
- Throughput: Over 13.9 million business frames and 227 million fill frames.
- Data Integrity: 0 CRC errors and 0 fingerprint mismatches across all hundreds of millions of frames.
- Driver Recovery: During this high-speed test, minor physical layer interference triggered the ERROR-PASSIVE state (TEC=128). However, the driver successfully recovered, and no Bus-Off was observed.

The complete test suite (C and Python) and raw test logs have been published for reproducibility and can be found here:

zlg python link: https://gist.github.com/AaronDot/e33f48c6c89d64e6b3564d9125ac2b82
linux C link: https://gist.github.com/AaronDot/6b7bbbc07a378fc263ccbc9f4c42e23a
500k+2M result link: https://gist.github.com/AaronDot/2ec489b1175d52f87bb9ba043168b80c
1M+4M result link: https://gist.github.com/AaronDot/a91fb52ffcec859b0eddc4f89b64eb3c

Link to V8:
https://lore.kernel.org/all/[email protected]/

V8:
Patch (1/2):
- Use local copy of can_bittiming in set_btr to avoid corrupting persistent structure;
- Fix endianness and strict aliasing in TX/RX data paths;
- Fixed spelling errors;
Patch (2/2):
- Add overflow detection for RXDMA;
- Simplified callback function names

Link to V7:
https://lore.kernel.org/all/[email protected]/

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 | 3075 ++++++++++++++++++++++++++++++
 4 files changed, 3094 insertions(+)
 create mode 100644 drivers/net/can/loongson_canfd.c

base-commit: 647b81ddefc6364290e67bf33c89d54971f8995e

2.52.0