Call skb_tx_timestamp() within can_put_echo_skb() so that a software
tx timestamp gets attached on the skb.
There two main reasons to include this call in can_put_echo_skb():
* It easily allow to enable the tx timestamp on all devices with
just one small change.
* According to Documentation/networking/timestamping.rst, the tx
timestamps should be generated in the device driver as close as
possible, but always prior to passing the packet to the network
interface. During the call to can_put_echo_skb(), the skb gets
cloned meaning that the driver should not dereference the skb
variable anymore after can_put_echo_skb() returns. This makes
can_put_echo_skb() the very last place we can use the skb without
having to access the echo_skb[] array.
Remark: by default, skb_tx_timestamp() does nothing. It needs to be
activated by passing the SOF_TIMESTAMPING_TX_SOFTWARE flag either
through socket options or control messages.
References:
* Support for the error queue in CAN RAW sockets (which is needed for
tx timestamps) was introduced in:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=eb88531bdbfaafb827192d1fc6c5a3fcc4fadd96
* Put the call to skb_tx_timestamp() just before adding it to the
array: https://lkml.org/lkml/2021/1/10/54
* About Tx hardware timestamps
https://lore.kernel.org/linux-can/20210111171152.GB11715@xxxxxxxxxxxxxxxxxx/
Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
---
drivers/net/can/dev/skb.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/net/can/dev/skb.c b/drivers/net/can/dev/skb.c
index 53683d4312f1..6a64fe410987 100644
--- a/drivers/net/can/dev/skb.c
+++ b/drivers/net/can/dev/skb.c
@@ -65,6 +65,8 @@ int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
/* save frame_len to reuse it when transmission is completed */
can_skb_prv(skb)->frame_len = frame_len;
+ skb_tx_timestamp(skb);
+
/* save this skb for tx interrupt echo handling */
priv->echo_skb[idx] = skb;
} else {
--
2.26.2
