linux-kernel - Re: [PATCH 09/10] pwm-backlight: Use an optional power supply

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Date:	Tue, 01 Oct 2013 14:59:43 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Thierry Reding <thierry.reding@...il.com>
CC:	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Tony Lindgren <tony@...mide.com>,
	Eric Miao <eric.y.miao@...il.com>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Ben Dooks <ben-linux@...ff.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>,
	Guan Xuetao <gxt@...c.pku.edu.cn>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
	openezx-devel@...ts.openezx.org, linux-samsung-soc@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-pwm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/10] pwm-backlight: Use an optional power supply

On 10/01/2013 02:53 PM, Thierry Reding wrote:
> On Tue, Oct 01, 2013 at 12:43:57PM -0600, Stephen Warren wrote:
>> On 09/23/2013 03:41 PM, Thierry Reding wrote:
>>> Many backlights require a power supply to work properly. This
>>> commit uses a power-supply regulator, if available, to power up
>>> and power down the panel.
>> 
>> I think that all backlights require a power supply, albeit the
>> supply may not be SW-controllable. Hence, shouldn't the regulator
>> be mandatory in the binding, yet the driver be defensively coded
>> such that if one isn't specified, the driver continues to work?
> 
> That has already changed in my local version of this patch.
> 
>>> diff --git a/drivers/video/backlight/pwm_bl.c
>>> b/drivers/video/backlight/pwm_bl.c
>> 
>>> @@ -253,6 +264,16 @@ static int pwm_backlight_probe(struct
>>> platform_device *pdev) } }
>>> 
>>> +	pb->power_supply = devm_regulator_get_optional(&pdev->dev,
>>> "power");
>> 
>> ... so I think that should be devm_regulator_get(), since the
>> regulator isn't really optional.
>> 
>>> +	if (IS_ERR(pb->power_supply)) { +		if
>>> (PTR_ERR(pb->power_supply) != -ENODEV) { +			ret =
>>> PTR_ERR(pb->power_supply); +			goto err_gpio; +		} + +
>>> pb->power_supply = NULL;
>> 
>> If devm_regulator_get_optional() returns an error value or a
>> valid value, then I don't think that this driver should transmute
>> error values into NULL; NULL might be a perfectly valid regulator
>> value. Related, I think the if (pb->power_supply) tests should be
>> replaced with if (!IS_ERR(pb->power_supply)) instead.
> 
> All of that is already done in my local tree. This actually turns
> out to work rather smoothly with the new support for optional
> regulators. The regulator core will give you a dummy regulator
> (assuming it's there physically but hasn't been wired up in
> software) that's always on, so the driver doesn't even have to
> special case it anymore.

OK, hopefully it (the regulator core) complains about the missing DT
property though; I assume you're using regulator_get() not
regulator_get_optional(), since the supply really is not optional.
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