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

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Date:	Wed, 6 Mar 2013 13:53:27 +0900
From:	Alex Courbot <acourbot@...dia.com>
To:	Andrew Chew <AChew@...dia.com>
CC:	"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 11:41 AM, Andrew Chew wrote:
>>>    struct pwm_bl_data {
>>>    	struct pwm_device	*pwm;
>>>    	struct device		*dev;
>>> +	struct regulator	*en_supply;
>>> +	bool			en_supply_enabled;
>>
>> Couldn't you use regulator_is_enabled() and get rid of en_supply_enabled?
>> It would also ensure the driver performs correctly no matter what the initial
>> state of the regulator is.
>
> Are you sure this works?  I'm concerned about the (bizarre and unlikely) case
> where this supply is shared with another driver, so I use en_supply_enabled
> to track the state of the supply such that I can ignore that case.

You're right, consumers can share regulators and the calls to 
enable/disable need to be balanced. Also there is no way to check the 
intensity of the backlight prior to the change to detect a transition, 
so I guess your approach is indeed the most appropriate here.

Alex.

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