linux-kernel - Re: [PATCH] regulator: core: Get and put regulator of

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Message-ID: <20140403111431.GU14763@sirena.org.uk>
Date:	Thu, 3 Apr 2014 12:14:31 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
Cc:	lgirdwood@...il.com, linux-kernel@...r.kernel.org,
	patches@...nsource.wolfsonmicro.com
Subject: Re: [PATCH] regulator: core: Get and put regulator of_node

On Thu, Apr 03, 2014 at 11:58:04AM +0100, Charles Keepax wrote:
> On Wed, Apr 02, 2014 at 05:53:54PM +0100, Mark Brown wrote:

> > To make this correct we need to at least ensure that the node passed
> > into the regulator API is valid and referenced at that time so there
> > should only be an issue for the core if the reference is dropped after
> > that.  In the above case the device model is holding a reference since
> > this is the of_node for the device itself so taking the reference won't
> > hurt but is redundant.  In cases where we have more than one regulator
> > and are using of_regulator_match() then things are more tricky.
> > Something needs to drop the references it returns (which isn't happening
> > at all at the minute).

> From what I can see of_regulator_match isn't taking any
> references at the minute? for_each_child_of_node will get a
> reference but it will also put that when we process the next
> child. We copy the pointer to the child into match->of_node
> but don't manually increment the reference at all. So
> of_regulator_match has no effect on the reference count of the
> of_node.

Right, so that needs fixing - like I say if there's no reference being
taken we already have a problem and taking another reference later on
isn't going to fix it.

> >  Doing it while doing the match and register
> > seems simple and neat from an error handling point of view so having the
> > core take an additional reference during the registration would join up
> > with that.

> The main issue I have is that devm_regualtor_register is a bit
> awkward. With regulator_register you will always be calling
> regulator_unregister so you can put the of_node there but with
> devm there isn't really a good place to put the of_node.

That's why I suggested it might be OK to take a reference in the core -
this would allow the device probe to safely drop its reference before it
returns.

> Would perhaps a sensible thing here be to add an of_node_get to
> of_regulator_match, since we seem to be expecting that to
> increase the ref count. And then just add an of_node_put to
> regulator_unregister. And for anything directly using
> regulator_register/devm_regulator_register they should add a
> manual of_node_get?

That seems very ugly.

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