linux-kernel - Re: [PATCH v3 1/1] can: dev: add software tx timestamps

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Date:   Tue, 12 Jan 2021 09:00:33 +0900
From:   Vincent MAILHOL <mailhol.vincent@...adoo.fr>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        linux-can <linux-can@...r.kernel.org>,
        Jeroen Hofstee <jhofstee@...tronenergy.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] can: dev: add software tx timestamps

On Tue. 12 Jan 2021 at 02:11, Richard Cochran <richardcochran@...il.com> wrote:
>
> On Sun, Jan 10, 2021 at 09:49:03PM +0900, Vincent Mailhol wrote:
> >   * 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.
>
> I can't agree with that statement.  The local loopback is a special
> "feature" of CAN sockets, and some programs turn it off.  Furthermore,
> requiring user space to handle CAN sockets differently WRT Tx time
> stamps is user-unfriendly.  So I would strongly support adding
> SOF_TIMESTAMPING_TX_HARDWARE to the CAN layer in the future.
>
> (This isn't a criticism of the current patch, though.)

Fair enough. Implementing SOF_TIMESTAMPING_TX_HARDWARE would
result into having the timestamp being duplicated for the
loopback frames but allowing existing programs to work as
with no modifications is a good enough reason.

Out of curiosity, which programs do you use? I guess wireshark
but please let me know if you use any other programs (I just use
to write a small C program to do the stuff).

Mark: do you want me to send a v4 of that patch with above
comment removed or can you directly do the change in your testing
branch?


Yours sincerely,
Vincent