linux-kernel - Re: [PATCH RFC V1 net-next 3/4] net: Let the active time stamping layer be selectable.

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Date:   Fri, 21 Jan 2022 12:05:22 +0100
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Vladimir Oltean <vladimir.oltean@....com>,
        Richard Cochran <richardcochran@...il.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Lunn <andrew@...n.ch>,
        David Miller <davem@...emloft.net>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Jakub Kicinski <kuba@...nel.org>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH RFC V1 net-next 3/4] net: Let the active time stamping
 layer be selectable.

On Thu Jan 20 2022, Vladimir Oltean wrote:
> Hi Richard,
>
> On Mon, Jan 03, 2022 at 03:25:54PM -0800, Richard Cochran wrote:
>> Make the sysfs knob writable, and add checks in the ioctl and time
>> stamping paths to respect the currently selected time stamping layer.
>> 
>> Signed-off-by: Richard Cochran <richardcochran@...il.com>
>> ---
>
> Could we think of a more flexible solution? Your proposal would not
> allow a packet to have multiple hwtstamps, and maybe that would be
> interesting for some use cases (hardware testing, mostly).

One use case i can think of for having multiple hwtimestamps per packet
is crosstimestamping. Some devices such as hellcreek have multiple PHCs
and allow generation of such crosstimestamps.

Thanks,
Kurt

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