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SubjectRe: [PATCH v3 1/1] can: dev: add software tx timestamps
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On 1/10/21 1:49 PM, Vincent Mailhol wrote:
> 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>

Applied to linux-can-next/testing (ontop of my dev infrastructure cleanup).

regards,
Marc

--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung West/Dortmund | Phone: +49-231-2826-924 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |

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