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From:   Chuhong Yuan <hslester96@gmail.com>
Date:   Mon, 12 Aug 2019 22:19:33 +0800
Message-ID: <CANhBUQ1QZUU9Fv+usQhUvs4ehy-OTTf2UWRKb333Bsfga=422Q@mail.gmail.com>
Subject: Re: [PATCH] regulator: core: Add devres versions of regulator_enable/disable
To:     Mark Brown <broonie@kernel.org>
Cc:     Liam Girdwood <lgirdwood@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Aug 12, 2019 at 8:51 PM Chuhong Yuan <hslester96@gmail.com> wrote:
>
> On Mon, Aug 12, 2019 at 7:07 PM Mark Brown <broonie@kernel.org> wrote:
> >
> > On Sat, Aug 10, 2019 at 09:44:45AM +0800, Chuhong Yuan wrote:
> > > On Fri, Aug 9, 2019 at 11:11 PM Mark Brown <broonie@kernel.org> wrote:
> >
> > > > I'm not super keen on managed versions of these functions since they're
> > > > very likely to cause reference counting issues between the probe/remove
> > > > path and the suspend/resume path which aren't obvious from the code, I'm
> > > > especially worried about double frees on release.
> >
> > > I find that 29 of 31 cases I found call regulator_disable() only when encounter
> > > probe failure or in .remove.
> > > So I think the devm versions of regulator_enable/disable() will not cause big
> > > problems.
> >
> > There's way more drivers using regulators than that...
> >
>
> I wrote a new coccinelle script to detect all regulator_disable() in .remove,
> 101 drivers are found in total.
> Within them, 25 drivers cannot benefit from devres version of regulator_enable()
> since they have additional non-devm operations after
> regulator_disable() in .remove.

I find 6 of 25 can benefit from devm_regulator_enable().
They are included in my previously found 147 cases so I incorrectly skipped them
while checking.
Therefore, there are 82 cases that can benefit from devm_regulator_enable() and
66 of them(80.5%) only call regulator_disable() when fail in probe or
in .remove.

> Within the left 76 cases, 60 drivers (79%) only use
> regulator_disable() when encounter
> probe failure or in .remove.
> The left 16 cases mostly use regulator_disable() in _suspend().
> Furthermore, 3 cases of 76 are found to forget to disable regulator
> when fail in probe.
> So I think a devres version of regulator_enable/disable() has more
> benefits than potential
> risk.
>
> > > I even found a driver to forget to disable regulator when encounter
> > > probe failure,
> > > which is drivers/iio/adc/ti-adc128s052.c.
> > > And a devm version of regulator_enable() can prevent such mistakes.
> >
> > Yes, it's useful for that.