linux-kernel - Re: [PATCH] backlight: add regulator support for platform

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Date:	Mon, 5 Dec 2011 10:52:02 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Thomas Abraham <thomas.abraham@...aro.org>
Cc:	Kyungmin Park <kmpark@...radead.org>, rpurdie@...ys.net,
	ben-linux@...ff.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	kgene.kim@...sung.com, patches@...aro.org,
	Linus Walleij <linus.walleij@...aro.org>,
	Rajendra Nayak <rnayak@...com>
Subject: Re: [PATCH] backlight: add regulator support for platform_lcd driver

On Mon, Dec 05, 2011 at 04:06:17PM +0530, Thomas Abraham wrote:
> On 5 December 2011 15:40, Kyungmin Park <kmpark@...radead.org> wrote:

> > Recent regulator discussion. it should be failed instead fall through
> > gracefully.

> Ok. But in this case, there could be boards that do not use a
> regulator for the lcd/display interface. Is it mandatory for fail if
> regulator is not found. Sorry, I have not read through the regulator
> discussion.

The boards should supply a fixed voltage regulator representing the
supply (or use CONFIG_REGULATOR_DUMMY to substitute in a dummy regulator
when not needed).  Sascha Hauer had some patches to add a flag that
could be set to enable this mode on init rather than through Kconfig but
they needed a bit of cleanup, not sure what the status is there.

> The constraint 'apply_uV' cannot be expressed with a device tree. So
> there has be a mechanism to set the required output voltage for a
> regulator.

It's not an option to not have it with device tree - if there's a single
voltage specified apply_uV is assumed.
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