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Date:   Sat, 7 Aug 2021 17:43:32 +0300
From:   Vladimir Oltean <olteanv@gmail.com>
To:     Richard Cochran <richardcochran@gmail.com>
Cc:     Vinicius Costa Gomes <vinicius.gomes@intel.com>,
        Yangbo Lu <yangbo.lu@nxp.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        mptcp@lists.linux.dev, "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Mat Martineau <mathew.j.martineau@linux.intel.com>,
        Matthieu Baerts <matthieu.baerts@tessares.net>,
        Shuah Khan <shuah@kernel.org>,
        Michal Kubecek <mkubecek@suse.cz>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Andrew Lunn <andrew@lunn.ch>, Rui Sousa <rui.sousa@nxp.com>,
        Sebastien Laveze <sebastien.laveze@nxp.com>
Subject: Re: [net-next, v5, 02/11] ptp: support ptp physical/virtual clocks
 conversion
Message-ID: <20210807144332.szyazdfl42abwzmd@skbuf>
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 <20210630081202.4423-3-yangbo.lu@nxp.com>
 <87r1f6kqby.fsf@vcostago-mobl2.amr.corp.intel.com>
 <20210807142259.GB22362@hoboy.vegasvil.org>
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On Sat, Aug 07, 2021 at 07:22:59AM -0700, Richard Cochran wrote:
> On Fri, Aug 06, 2021 at 06:15:29PM -0700, Vinicius Costa Gomes wrote:
> 
> > >  int ptp_clock_unregister(struct ptp_clock *ptp)
> > >  {
> > > +	if (ptp_vclock_in_use(ptp)) {
> > > +		pr_err("ptp: virtual clock in use\n");
> > > +		return -EBUSY;
> > > +	}
> > > +
> > 
> > None of the drivers (that I looked) expect ptp_clock_unregister() to
> > return an error.
> > 
> > So, what should we do?
> >  1. Fix all the drivers to return an error on module unloading (that's
> >  usually the path ptp_clock_unregister() is called)?
> >  2. Remove all the PTP virtual clocks when the physical clock is
> >  unregistered?
> 
> This:
> 
>  3. Let the vclocks hold a reference to the underlying posix dynamic clock.

So even if the vclock holds a reference to the underlying POSIX clock,
that won't prevent the hardware driver from unbinding, and further
gettime() calls on the vclock from faulting, will it?

What about:

4. Create a device link with the vclock being a consumer and the parent
   clock being a supplier? This way, ptp_vclock_unregister() is
   automatically called whenever (and before) ptp_clock_unregister() is.

https://www.kernel.org/doc/html/latest/driver-api/device_link.html