As Jacob noticed, the optimization introduced in 387da6bc7a82 ("can: c_can: cache frames to operate as a true FIFO") doesn't properly work on C_CAN, but on D_CAN IP cores. The exact reasons are still unknown.

For now disable caching if CAN frames in the TX path for C_CAN cores.

Fixes: 387da6bc7a82 ("can: c_can: cache frames to operate as a true FIFO") Link: https://lore.kernel.org/all/20220928083354.1062321-1-mkl@pengutronix.de Link: https://lore.kernel.org/all/15a8084b-9617-2da1-6704-d7e39d60643b@gmail.com Reported-by: Jacob Kroon jacob.kroon@gmail.com Tested-by: Jacob Kroon jacob.kroon@gmail.com Cc: stable@vger.kernel.org # v5.15 Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de --- drivers/net/can/c_can/c_can.h | 17 +++++++++++++++-- drivers/net/can/c_can/c_can_main.c | 11 +++++------ 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h index f23a03300a81..029cd8194ed5 100644 --- a/drivers/net/can/c_can/c_can.h +++ b/drivers/net/can/c_can/c_can.h @@ -235,9 +235,22 @@ static inline u8 c_can_get_tx_tail(const struct c_can_tx_ring *ring) return ring->tail & (ring->obj_num - 1); }

-static inline u8 c_can_get_tx_free(const struct c_can_tx_ring *ring) +static inline u8 c_can_get_tx_free(const struct c_can_priv *priv, + const struct c_can_tx_ring *ring) { - return ring->obj_num - (ring->head - ring->tail); + u8 head = c_can_get_tx_head(ring); + u8 tail = c_can_get_tx_tail(ring); + + if (priv->type == BOSCH_D_CAN) + return ring->obj_num - (ring->head - ring->tail); + + /* This is not a FIFO. C/D_CAN sends out the buffers + * prioritized. The lowest buffer number wins. + */ + if (head < tail) + return 0; + + return ring->obj_num - head; }

#endif /* C_CAN_H */ diff --git a/drivers/net/can/c_can/c_can_main.c b/drivers/net/can/c_can/c_can_main.c index dc8132862f33..d6605dbb7737 100644 --- a/drivers/net/can/c_can/c_can_main.c +++ b/drivers/net/can/c_can/c_can_main.c @@ -429,7 +429,7 @@ static void c_can_setup_receive_object(struct net_device *dev, int iface, static bool c_can_tx_busy(const struct c_can_priv *priv, const struct c_can_tx_ring *tx_ring) { - if (c_can_get_tx_free(tx_ring) > 0) + if (c_can_get_tx_free(priv, tx_ring) > 0) return false;

netif_stop_queue(priv->dev); @@ -437,7 +437,7 @@ static bool c_can_tx_busy(const struct c_can_priv *priv, /* Memory barrier before checking tx_free (head and tail) */ smp_mb();

- if (c_can_get_tx_free(tx_ring) == 0) { + if (c_can_get_tx_free(priv, tx_ring) == 0) { netdev_dbg(priv->dev, "Stopping tx-queue (tx_head=0x%08x, tx_tail=0x%08x, len=%d).\n", tx_ring->head, tx_ring->tail, @@ -465,7 +465,7 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,

idx = c_can_get_tx_head(tx_ring); tx_ring->head++; - if (c_can_get_tx_free(tx_ring) == 0) + if (c_can_get_tx_free(priv, tx_ring) == 0) netif_stop_queue(dev);

if (idx < c_can_get_tx_tail(tx_ring)) @@ -748,7 +748,7 @@ static void c_can_do_tx(struct net_device *dev) return;

tx_ring->tail += pkts; - if (c_can_get_tx_free(tx_ring)) { + if (c_can_get_tx_free(priv, tx_ring)) { /* Make sure that anybody stopping the queue after * this sees the new tx_ring->tail. */ @@ -760,8 +760,7 @@ static void c_can_do_tx(struct net_device *dev) stats->tx_packets += pkts;

tail = c_can_get_tx_tail(tx_ring); - - if (tail == 0) { + if (priv->type == BOSCH_D_CAN && tail == 0) { u8 head = c_can_get_tx_head(tx_ring);

/* Start transmission for all cached messages */

base-commit: 44d70bb561dac9363f45787aa93dfca36877ee01