linux-kernel - Re: [PATCH] pwm-backlight: add regulator and GPIO support

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Message-ID: <20120704122733.GA30698@sirena.org.uk>
Date:	Wed, 4 Jul 2012 13:27:33 +0100
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	Sascha Hauer <s.hauer@...gutronix.de>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH] pwm-backlight: add regulator and GPIO support

On Wed, Jul 04, 2012 at 09:26:58PM +0900, Alex Courbot wrote:
> On 07/04/2012 07:48 PM, Sascha Hauer wrote:>> +

> > This looses several resources allocated earlier, like the enable gpio
> > and the pwm. This is really bad here since I have no regulator specified
> > and devm_regulator_get returns with -EPROBE_DEFER. Next time the core
> > tries to probe the driver the driver bails out because the gpio and the
> > pwm is already requested.

> That's very bad indeed. I assumed that the kernel would free
> devm-allocated resources after probe returned -EPROBE_DEFER, so that
> probe could reallocate them the next time it is called. Apparently
> that was wrong. Do you know what would the right approach be in this
> case? Does the kernel preserve the device structure and its
> associated data between the two calls to probe? If so, I could just
> check whether the private data has already been constructed to know
> which state we are in and continue from there.

I'd really expect the devm_ functions to behave as you expect - if they
don't currently we should probably fix them so that they do otherwise
we're going to be in for a lot of surprises and probe deferral becomes a
lot more cumbersome to use.
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