can: c_can: don't cache TX messages for C_CAN cores

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>

diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
index f23a03300a81e365d0999db9a291b73c13808b86..029cd8194ed54e7707ee8cabb9fe6ac91435451c 100644 (file)
--- 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 dc8132862f333aff1b034a11853bcaf506654b8f..d6605dbb7737bb7227301e8760d00a86fd78c3a7 100644 (file)
--- 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 */