linux-kernel - Re: [PATCH] backlight: lcd: add driver for raster-type lcd's with gpio controlled panel reset

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Message-ID: <20120106064929.GB3496@opensource.wolfsonmicro.com>
Date:	Thu, 5 Jan 2012 22:49:30 -0800
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Thomas Abraham <thomas.abraham@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	rpurdie@...ys.net, linux-samsung-soc@...r.kernel.org,
	grant.likely@...retlab.ca, rob.herring@...xeda.com,
	kgene.kim@...sung.com, jg1.han@...sung.com,
	kyungmin.park@...sung.com, cbou@...l.ru, kwangwoo.lee@...il.com,
	augulis.darius@...il.com, ben-linux@...ff.org, patches@...aro.org
Subject: Re: [PATCH] backlight: lcd: add driver for raster-type lcd's with
 gpio controlled panel reset

On Thu, Jan 05, 2012 at 08:07:53PM +0100, Lars-Peter Clausen wrote:

> > +- lcd,pwrctrl-min-uV: If a regulator controls the Vcc voltage of the lcd panel,
> > +  this property specifies the minimum voltage the regulator should supply.
> > +  The value of this property should in in micro-volts.
> > +- lcd,pwrctrl-max-uV: If a regulator controls the Vcc voltage of the lcd panel,
> > +  this property specifies the maximum voltage the regulator should limit to
> > +  on the Vcc line. The value of this property should in in micro-volts.

> The min and max voltage should rather be specified through the regulator
> constraints.

In principle it should be specified in both places to account for shared
supplies though for all practical purposes for an LCD panel I can't see
multiple users sharing the same regulator and varying the voltage at
runtime.

> > +	if (lcd_enable) {
> > +		if ((pd->min_uV || pd->max_uV) &&
> > +			regulator_set_voltage(lp->regulator,
> > +						pd->min_uV, pd->max_uV))
> > +				dev_info(lp->dev,
> > +					"regulator voltage set failed\n");
> > +		if (regulator_enable(lp->regulator))
> > +			dev_info(lp->dev, "failed to enable regulator\n");
> > +	} else {
> > +		regulator_disable(lp->regulator);
> > +	}

> I think you have to make sure that the regulator enable and disable calls are
> balanced.

Yes.

> > +#ifdef CONFIG_OF

> I think you can remove all the CONFIG_OF ifdefs, the of API should stub itself out.

It's reasonably idiomatic to do this if the parsing code is in a
separate function.
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