On Tue, 12 Jan 2021 17:46:25 -0800 Jakub Kicinski wrote:

On Tue, 12 Jan 2021 11:03:00 +0100 Marc Kleine-Budde wrote:

quoted

On 1/12/21 10:54 AM, Vincent Mailhol wrote:  

quoted

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@hoboy.vegasvil.org/ (local)

Signed-off-by: Vincent Mailhol <redacted>    

Applied to linux-can-next/testing  

Please make sure to address the warnings before this hits net-next:

https://patchwork.kernel.org/project/netdevbpf/patch/20210112130538.14912-2-mailhol.vincent@wanadoo.fr/

Actually it appears not to build with allmodconfig..?

Erm, apologies, I confused different CAN patches, this one did not get
build tested.