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

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Date:	Wed, 6 Mar 2013 13:56:40 +0900
From:	Alex Courbot <acourbot@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
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 03/06/2013 01:20 PM, Stephen Warren wrote:
> 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.

That's good to know, thanks. So does this mean that Andrew should make 
the enable regulator mandatory and update current users to provide a 
dummy one?

Alex.

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