Re: [RESEND PATCH 4/4] can: c_can: cache frames to operate as a true FIFO

Hi Marc,

Il 04/08/2021 11:45 Marc Kleine-Budde [off-list ref] ha scritto:

 
On 25.07.2021 18:11:50, Dario Binacchi wrote:

quoted

diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
index 8fe7e2138620..fc499a70b797 100644
--- a/drivers/net/can/c_can/c_can.h
+++ b/drivers/net/can/c_can/c_can.h

@@ -200,6 +200,7 @@ struct c_can_priv {
 	atomic_t sie_pending;
 	unsigned long tx_dir;
 	int last_status;
+	spinlock_t tx_lock;

What does the spin lock protect?

quoted

 	struct c_can_tx_ring tx;
 	u16 (*read_reg)(const struct c_can_priv *priv, enum reg index);
 	void (*write_reg)(const struct c_can_priv *priv, enum reg index, u16 val);

@@ -236,4 +237,9 @@ 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)
+{
+	return ring->obj_num - (ring->head - ring->tail);
+}
+
 #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 451ac9a9586a..4c061fef002c 100644
--- a/drivers/net/can/c_can/c_can_main.c
+++ b/drivers/net/can/c_can/c_can_main.c

@@ -427,20 +427,6 @@ static void c_can_setup_receive_object(struct net_device *dev, int iface,
 	c_can_object_put(dev, iface, obj, IF_COMM_RCV_SETUP);
 }
 
-static u8 c_can_get_tx_free(const struct c_can_tx_ring *ring)
-{
-	u8 head = c_can_get_tx_head(ring);
-	u8 tail = c_can_get_tx_tail(ring);
-
-	/* 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;
-}
-
 static bool c_can_tx_busy(const struct c_can_priv *priv,
 			  const struct c_can_tx_ring *tx_ring)
 {

@@ -470,7 +456,7 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
 	struct can_frame *frame = (struct can_frame *)skb->data;
 	struct c_can_priv *priv = netdev_priv(dev);
 	struct c_can_tx_ring *tx_ring = &priv->tx;
-	u32 idx, obj;
+	u32 idx, obj, cmd = IF_COMM_TX;
 
 	if (can_dropped_invalid_skb(dev, skb))
 		return NETDEV_TX_OK;

@@ -483,7 +469,11 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
 	if (c_can_get_tx_free(tx_ring) == 0)
 		netif_stop_queue(dev);
 
-	obj = idx + priv->msg_obj_tx_first;
+	spin_lock_bh(&priv->tx_lock);

What does the spin_lock protect? The ndo_start_xmit function is properly
serialized by the networking core.

The spin_lock protects the access to the IF_TX interface. Enabling the transmission 
of cached messages occur inside interrupt and the use of the IF_RX interface,
which would avoid the use of the spinlock, has not been validated by
the tests.

Thanks and regards,
Dario

Otherwise the patch looks good!

Marc

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