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

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Date:   Mon, 11 Jan 2021 09:11:52 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Vincent Mailhol <mailhol.vincent@...adoo.fr>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>, 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 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.)

Thanks,
Richard