Messages in this thread Patch in this message | | | From | Vincent Mailhol <> | Subject | [PATCH v2 1/1] can: dev: add software tx timestamps | Date | Sun, 10 Jan 2021 21:41:31 +0900 |
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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.
Remarks:
* 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.
* The hardware rx timestamp of a local loopback message is the hardware tx timestamp. This means that there are no needs to implement SOF_TIMESTAMPING_TX_HARDWARE for CAN sockets.
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
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> --- drivers/net/can/dev.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c index 3486704c8a95..3904e0874543 100644 --- a/drivers/net/can/dev.c +++ b/drivers/net/can/dev.c @@ -484,6 +484,8 @@ int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev, /* save this skb for tx interrupt echo handling */ priv->echo_skb[idx] = skb; + + skb_tx_timestamp(skb); } else { /* locking problem with netif_stop_queue() ?? */ netdev_err(dev, "%s: BUG! echo_skb %d is occupied!\n", __func__, idx); -- 2.26.2
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