netdev - Re: [PATCH 1/1] net: fec: ptp: avoid register access when ipg clock is disabled

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Message-ID: <20210223142726.GA4711@hoboy.vegasvil.org>
Date:   Tue, 23 Feb 2021 06:27:26 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Heiko Thiery <heiko.thiery@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Fugang Duan <fugang.duan@....com>
Subject: Re: [PATCH 1/1] net: fec: ptp: avoid register access when ipg clock
 is disabled

On Tue, Feb 23, 2021 at 09:00:32AM +0100, Heiko Thiery wrote:
> HI Jakub,
> 
> Am Di., 23. Feb. 2021 um 04:00 Uhr schrieb Jakub Kicinski <kuba@...nel.org>:
> > Why is the PTP interface registered when it can't be accessed?
> >
> > Perhaps the driver should unregister the PTP clock when it's brought
> > down?

I don't see any reason why a clock should stop ticking just because
the interface is down.  This is a poor driver design, but sadly it
gets copied and even defended.

> Good question, but I do not know what happens e.g. with linuxptp when
> the device that was opened before will be gone.

If a network interface goes down, ptp4l will notice via rtnl and close
the interface.  Then it re-opens the sockets on rtnl up.  However, the
file descriptor representing the dynamic posix clock stays opened.

Thanks,
Richard