linux-kernel - Re: [PATCH] backlight: add regulator support for platform

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Message-ID: <CAJuYYwTT2jbbquZM=ZwK=Gh39ss=iG0WDCc3TYjzHLEgfeC1gA@mail.gmail.com>
Date:	Mon, 5 Dec 2011 16:06:17 +0530
From:	Thomas Abraham <thomas.abraham@...aro.org>
To:	Kyungmin Park <kmpark@...radead.org>
Cc:	rpurdie@...ys.net, ben-linux@...ff.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, kgene.kim@...sung.com,
	patches@...aro.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Rajendra Nayak <rnayak@...com>
Subject: Re: [PATCH] backlight: add regulator support for platform_lcd driver

Dear Mr. Park,

On 5 December 2011 15:40, Kyungmin Park <kmpark@...radead.org> wrote:
[...]

>> +     /*
>> +      * If power to lcd and/or lcd interface is controlled using a regulator,
>> +      * enable or disable the regulator based in the power setting.
>> +      */
>> +     lcd_regulator = regulator_get(plcd->us, "vcc_lcd");
>> +     if (IS_ERR(lcd_regulator)) {
>> +             dev_info(plcd->us, "could not get regulator\n");
>> +             goto set_power;
>> +     }
>
> Recent regulator discussion. it should be failed instead fall through
> gracefully.

Ok. But in this case, there could be boards that do not use a
regulator for the lcd/display interface. Is it mandatory for fail if
regulator is not found. Sorry, I have not read through the regulator
discussion.

>> +
>> +     if (lcd_power) {
>> +             if (plcd->pdata->min_uV || plcd->pdata->max_uV)
>> +                     if (regulator_set_voltage(lcd_regulator,
>> +                             plcd->pdata->min_uV, plcd->pdata->max_uV))
>> +                             dev_info(plcd->us,
>> +                                     "regulator voltage set failed\n");
> Are there case to change the voltage? Doesn't it easy to set the
> voltage at board file? I mean don't need to setup at drivers?

The constraint 'apply_uV' cannot be expressed with a device tree. So
there has be a mechanism to set the required output voltage for a
regulator.

In case of platform-lcd driver, the power source should be turned off
to the lcd/interfaces until the display controller driver is enabled.
Powering on the lcd/interfaces at boot time by default would not be
ideal.

Thanks for your review and comments.

Regards,
Thomas.

>
> Thank you,
> Kyungmin Park

[...]
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