linux-kernel - Re: [PATCH 1/1 v3] pwm_bl: Add support for backlight enable regulator

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Date:	Tue, 05 Mar 2013 21:20:51 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Alex Courbot <acourbot@...dia.com>
CC:	Andrew Chew <achew@...dia.com>,
	"thierry.reding@...onic-design.de" <thierry.reding@...onic-design.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1 v3] pwm_bl: Add support for backlight enable regulator

On 03/05/2013 07:18 PM, Alex Courbot wrote:
> On 03/06/2013 08:51 AM, Andrew Chew wrote:
>> The backlight enable regulator is specified in the device tree node for
>> backlight.

>> diff --git a/include/linux/pwm_backlight.h

>>   struct platform_pwm_backlight_data {
>>       int pwm_id;
>> +    struct regulator *en_supply;
> 
> You should not have this here. Platform data is supposed to provide the
> necessary information for the driver to resolve the resource - not the
> resource itself.
...
> There is one catch though: in case you don't want to use a regulator,
> and thus have none defined, regulator_get() will return -EPROBE_DEFER,
> so you cannot distinguish between "no regulator needed" and "supplier
> not ready yet" and your driver will always *require* a regulator. So at
> the end of the day you might still need a "use_enable_regulator" in the
> platform data to explicitly ask for probe() to look for it. This
> variable would also be set by parse_dt() if the "enable-supply" property
> exists.

A driver that requires a regulator always requires that regulator. If a
particular board doesn't have SW control over the power source, you're
supposed to provide a dummy (fixed) regulator so that the driver doesn't
care about the difference.
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