netdev - Re: [net-next 03/15] net/mlx5: Add adjphase function to support hardware-only offset control

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Message-ID: <Y8336MEkd6R/XU7x@hoboy.vegasvil.org>
Date:   Sun, 22 Jan 2023 18:58:48 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Rahul Rameshbabu <rrameshbabu@...dia.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Saeed Mahameed <saeed@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>, netdev@...r.kernel.org,
        Tariq Toukan <tariqt@...dia.com>,
        Gal Pressman <gal@...dia.com>,
        Vincent Cheng <vincent.cheng.xh@...esas.com>
Subject: Re: [net-next 03/15] net/mlx5: Add adjphase function to support
 hardware-only offset control

On Sun, Jan 22, 2023 at 06:48:49PM -0800, Rahul Rameshbabu wrote:

> Another question then is can adjtime/ADJ_SETOFFSET make use of this
> servo implementation on the device or is there a strict expectation that
> adjtime/ADJ_SETOFFSET is purely a function that adds the offset to the
> current current time?

ADJ_SETOFFSET == clock_settime.  Drivers should set the time
immediately.

> If adjphase is implemented by a driver, should
> ADJ_SETOFFSET try to make use of it in the ptp stack if the offset
> provided is supported by the adjphase implementation?

No.


BTW, as mentioned in the thread, the KernelDoc is really, really bad:

 * @adjphase:  Adjusts the phase offset of the hardware clock.
 *             parameter delta: Desired change in nanoseconds.

The change log is much better:

    ptp: Add adjphase function to support phase offset control.

    Adds adjust phase function to take advantage of a PHC
    clock's hardware filtering capability that uses phase offset
    control word instead of frequency offset control word.

So the Kernel Doc should say something like:

 * @adjphase:  Feeds the given phase offset into the hardware clock's servo.
 *             parameter delta: Measured phase offset in nanoseconds.

Thanks,
Richard