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From: Mark Brown <email@example.com>
To: Doug Anderson <firstname.lastname@example.org>
Cc: email@example.com, Axel Lin <firstname.lastname@example.org>,
Dmitry Torokhov <email@example.com>,
Olof Johansson <firstname.lastname@example.org>,
Javier Martinez Canillas <email@example.com>,
Paul Stewart <firstname.lastname@example.org>,
Liam Girdwood <email@example.com>,
Subject: Re: [PATCH] regulator: core: Fix enable GPIO reference counting
Date: Tue, 3 Mar 2015 14:23:11 +0000 [thread overview]
Message-ID: <20150303142311.GT21293@sirena.org.uk> (raw)
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On Mon, Mar 02, 2015 at 01:13:56PM -0800, Doug Anderson wrote:
> On Mon, Mar 2, 2015 at 10:47 AM, Mark Brown <firstname.lastname@example.org> wrote:
> > Looking at the code it seems that you're adding checks to skip calls in
> > the standard enable and disable paths but not touching other paths,
> > based on this patch by itself I can't tell if this is a good idea or
> > not. It certainly doesn't feel robust - if we're missing reference
> > counting skipping operations seems likely to lead to other bugs popping
> > up elsewhere when the other user that isn't doing a disable currently
> > decides to start doing so.
> I guess it depends on whether _regulator_do_enable() on an
> already-enabled rdev is supposed to be a noop or not. My assumption
> was that it was supposed to be a noop with reference counting handled
> by _regulator_enable().
Yes, that's the point.
> My assumption is that regulator drivers themselves shouldn't do
> reference counting. That is: if you call
> rdev->desc->ops->enable(rdev) twice you should not have to call
> rdev->desc->ops->disable(rdev) twice to disable. Right? That means
> my fix is making the "ena_pin" symmetric to how normal regulator
> drivers work.
> The refcounting being skipped by my patch is refcounting that's used
> only when the same GPIO is shared by more than one regulator. That
> is, if "vcc_a" uses GPIO1 and "vcc_b" also uses "GPIO1" we need
> refcounting. GPIO1 will be in the "on" state if either vcc_a or vcc_b
> is on. The problem came in because _regulator_do_enable() was
> incrementing the shared refcount every time it was called even if the
> specific regulator was already on.
This is all analysis which should have been in the changelog...
possibly not quite so verbosely but it should be there.
> Anyway, I looked at Javier's patch and it's also fine / reasonable.
> ...and in fact I would argue that possibly we could take both patches.
> Javier's patch eliminates the one known place where
> _regulator_do_enable() is called for an already-enabled regulator and
> my patch means that if someone else adds a new call we won't end up
> back in this same subtle bug. I'm happy to update the CL desc to make
> it more obvious if you'd like.
Yes, the changelog definitely needs to be *much* clearer. Especially
for things like locking and reference counting the changelog needs to
explain what the fix is and why it's safe, without that working it is a
lot harder to do a review as the reviewer needs to go back and check
that everything has been thought through properly.
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next prev parent reply other threads:[~2015-03-03 14:45 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-27 19:41 Doug Anderson
2015-02-27 20:08 ` Greg KH
2015-02-27 21:01 ` Javier Martinez Canillas
2015-03-02 18:57 ` Mark Brown
2015-03-02 20:21 ` Javier Martinez Canillas
2015-03-03 14:24 ` Mark Brown
2015-03-02 18:47 ` Mark Brown
2015-03-02 21:13 ` Doug Anderson
2015-03-03 14:23 ` Mark Brown [this message]
2015-03-03 23:21 ` Doug Anderson
2015-03-04 11:27 ` Mark Brown
2015-03-04 17:13 ` Doug Anderson
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