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

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Message-ID: <20120705064742.GL30009@pengutronix.de>
Date:	Thu, 5 Jul 2012 08:47:42 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	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 Thu, Jul 05, 2012 at 03:25:44PM +0900, Alex Courbot wrote:
> On 07/05/2012 03:20 PM, Sascha Hauer wrote:
> >>Oh, that is a mistake of mine then. Driver probe should continue if
> >>no regulator is declared (but should fail if some other error
> >>occured). I want to maintain backward compatibility with current
> >>users of the driver, so regulator/gpio specification should be
> >>optional.
> >
> >I think the only way doing this is to add a flag to platform_data. I
> >don't know if that's accepted though.
> 
> I thought about just checking if devm_get_regulator returned -ENODEV
> and happily continue if that was the case, assuming no regulator was
> declared.

And that's the problem. The get_regulator won't return -ENODEV. It will
return -EPROBE_DEFER which tells you nothing about whether a regulator
will ever be available or not.

Having a flag in platform data would be fine with me, but I know other
people think differently.

BTW in devicetree this flag implicitely exists with the power-supply
property. The regulator core could look if a power-supply property
is given and

- if it is given, a regulator is mandatory and the core either
  returns the regulator or -EPROBE_DEFER if it cannot find one.
- If it is not given, there is no regulator and the core could either
  return a special error code or a dummy regulator.

Right now the regulator core will just return -EPROBE_DEFER in both
cases. This could easily be changed in the regulator core.

Sascha

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