[PATCH net] can: c_can: don't cache TX messages for C_CAN cores

[PATCH net] can: c_can: don't cache TX messages for C_CAN cores

[Marc Kleine-Budde]

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
-- 
2.35.1

Re: [PATCH net] can: c_can: don't cache TX messages for C_CAN cores

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (master)
by Marc Kleine-Budde <mkl@pengutronix.de>:

On Wed, 28 Sep 2022 11:06:29 +0200 you wrote:
> 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>
> 
> [...]

Here is the summary with links:
  - [net] can: c_can: don't cache TX messages for C_CAN cores
    https://git.kernel.org/netdev/net/c/81d192c2ce74

You are awesome, thank you!
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