Merge tag 'linux-can-fixes-for-6.0-20220928' of...

Merge tag 'linux-can-fixes-for-6.0-20220928' of git://git.kernel.org/pub/scm/linux/kernel/git/mkl/linux-can

Marc Kleine-Budde says:

====================
pull-request: can 2022-09-28

The patch is by me and targets the c_can driver. It disables an
optimization in the TX path of C_CAN cores which causes problems.

* tag 'linux-can-fixes-for-6.0-20220928' of git://git.kernel.org/pub/scm/linux/kernel/git/mkl/linux-can:
  can: c_can: don't cache TX messages for C_CAN cores
====================

Link: https://lore.kernel.org/r/20220928090629.1124190-1-mkl@pengutronix.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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)
 {
+	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 */

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 */