can: do not increase tx_bytes statistics for RTR frames

The actual payload length of the CAN Remote Transmission Request (RTR)
frames is always 0, i.e. no payload is transmitted on the wire.
However, those RTR frames still use the DLC to indicate the length of
the requested frame.

As such, net_device_stats::tx_bytes should not be increased when
sending RTR frames.

The function can_get_echo_skb() already returns the correct length,
even for RTR frames (c.f. [1]). However, for historical reasons, the
drivers do not use can_get_echo_skb()'s return value and instead, most
of them store a temporary length (or dlc) in some local structure or
array. Using the return value of can_get_echo_skb() solves the
issue. After doing this, such length/dlc fields become unused and so
this patch does the adequate cleaning when needed.

This patch fixes all the CAN drivers.

Finally, can_get_echo_skb() is decorated with the __must_check
attribute in order to force future drivers to correctly use its return
value (else the compiler would emit a warning).

[1] commit ed3320cec279 ("can: dev: __can_get_echo_skb():
fix real payload length return value for RTR frames")

Link: https://lore.kernel.org/all/20211207121531.42941-6-mailhol.vincent@wanadoo.fr
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Ludovic Desroches <ludovic.desroches@microchip.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Chen-Yu Tsai <wens@csie.org>
Cc: Jernej Skrabec <jernej.skrabec@gmail.com>
Cc: Yasushi SHOJI <yashi@spacecubics.com>
Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Stephane Grosjean <s.grosjean@peak-system.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Tested-by: Jimmy Assarsson <extja@kvaser.com> # kvaser
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Stefan Mätje <stefan.maetje@esd.eu> # esd_usb2
Tested-by: Stefan Mätje <stefan.maetje@esd.eu> # esd_usb2
[mkl: add conversion for grcan]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 2 insertions, 15 deletions

diff --git a/drivers/net/can/grcan.c b/drivers/net/can/grcan.c
index 1b8ef97e4139..d0c5a7a60daf 100644
--- a/drivers/net/can/grcan.c
+++ b/drivers/net/can/grcan.c
@@ -255,7 +255,6 @@ struct grcan_priv {
 	struct grcan_dma dma;
 
 	struct sk_buff **echo_skb;	/* We allocate this on our own */
-	u8 *txdlc;			/* Length of queued frames */
 
 	/* The echo skb pointer, pointing into echo_skb and indicating which
 	 * frames can be echoed back. See the "Notes on the tx cyclic buffer
@@ -515,9 +514,7 @@ static int catch_up_echo_skb(struct net_device *dev, int budget, bool echo)
 		if (echo) {
 			/* Normal echo of messages */
 			stats->tx_packets++;
-			stats->tx_bytes += priv->txdlc[i];
-			priv->txdlc[i] = 0;
-			can_get_echo_skb(dev, i, NULL);
+			stats->tx_bytes += can_get_echo_skb(dev, i, NULL);
 		} else {
 			/* For cleanup of untransmitted messages */
 			can_free_echo_skb(dev, i, NULL);
@@ -1062,16 +1059,10 @@ static int grcan_open(struct net_device *dev)
 	priv->can.echo_skb_max = dma->tx.size;
 	priv->can.echo_skb = priv->echo_skb;
 
-	priv->txdlc = kcalloc(dma->tx.size, sizeof(*priv->txdlc), GFP_KERNEL);
-	if (!priv->txdlc) {
-		err = -ENOMEM;
-		goto exit_free_echo_skb;
-	}
-
 	/* Get can device up */
 	err = open_candev(dev);
 	if (err)
-		goto exit_free_txdlc;
+		goto exit_free_echo_skb;
 
 	err = request_irq(dev->irq, grcan_interrupt, IRQF_SHARED,
 			  dev->name, dev);
@@ -1093,8 +1084,6 @@ static int grcan_open(struct net_device *dev)
 
 exit_close_candev:
 	close_candev(dev);
-exit_free_txdlc:
-	kfree(priv->txdlc);
 exit_free_echo_skb:
 	kfree(priv->echo_skb);
 exit_free_dma_buffers:
@@ -1129,7 +1118,6 @@ static int grcan_close(struct net_device *dev)
 	priv->can.echo_skb_max = 0;
 	priv->can.echo_skb = NULL;
 	kfree(priv->echo_skb);
-	kfree(priv->txdlc);
 
 	return 0;
 }
@@ -1447,7 +1435,6 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
 	 * can_put_echo_skb would be an error unless other measures are
 	 * taken.
 	 */
-	priv->txdlc[slotindex] = cf->len; /* Store dlc for statistics */
 	can_put_echo_skb(skb, dev, slotindex, 0);
 
 	/* Make sure everything is written before allowing hardware to