linux-kernel - Re: [PATCH] regulator: wm8994: Use PROBE_FORCE

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Date:   Fri, 24 Mar 2023 09:23:53 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Doug Anderson <dianders@...omium.org>
CC:     Marek Szyprowski <m.szyprowski@...sung.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-samsung-soc@...r.kernel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        <patches@...nsource.cirrus.com>
Subject: Re: [PATCH] regulator: wm8994: Use PROBE_FORCE_SYNCHRONOUS

On Thu, Mar 23, 2023 at 11:00:32AM -0700, Doug Anderson wrote:
> Hi,
> 
> On Thu, Mar 23, 2023 at 10:45 AM Charles Keepax
> <ckeepax@...nsource.cirrus.com> wrote:
> >
> > I think really the best place to look at this would be at the
> > regulator level. It is fine if mfd_add_devices passes, the problem
> > really is that the regulator core doesn't realise the regulator is
> > going to be arriving, and thus returns a dummy regulator, rather
> > than returning EPROBE_DEFER. If it did the MFD driver would probe
> > defer at the point of requesting the regulator, which would all
> > make sense.
> 
> I think something like your suggestion could be made to work for the
> "microphone" supply in the arizona MFD, but not for the others looked
> at here.
> 
> The problem is that if the MFD driver gets -EPROBE_DEFER then it will
> go through its error handling path and call mfd_remove_devices().
> That'll remove the sub-device providing the regulator. If you try
> again, you'll just do the same. :-)
> 
> Specifically in wm8994 after we've populated the regulator sub-devices
> then we turn them on and start talking to the device.
> 
> I think the two options I have could both work for wm8994's case:
> either add some type of "my children have done probing" to MFD and
> move the turning on of regulators / talking to devices there, or add
> another stub-device and add it there. ;-)

Is this true if we keep the regulator as sync though? Yes it will
remove the children but when it re-adds them the reason that the
regulator probe deferred in the first place will hopefully be
removed. So it will now fully probe in path.

Thanks,
Charles