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

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Date:   Tue, 23 Feb 2021 16:04:16 +0100
From:   Heiko Thiery <heiko.thiery@...il.com>
To:     Richard Cochran <richardcochran@...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

Hi Richard,

Am Di., 23. Feb. 2021 um 15:27 Uhr schrieb Richard Cochran
<richardcochran@...il.com>:
>
> 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.

It is not only the PHC clock that stops. Rather, it is the entire
ethernet building block in the SOC that is disabled, including the
PHC.

> > 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,

-- 
Heiko