linux-kernel - Re: [PATCH v3] backlight: corgi_lcd: Use gpio_set_value_cansleep() to avoid WARN

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Date:	Wed, 05 Dec 2012 10:17:58 +0900
From:	Jingoo Han <jg1.han@...sung.com>
To:	'Andrew Morton' <akpm@...ux-foundation.org>
Cc:	'LKML' <linux-kernel@...r.kernel.org>,
	'Marko Katic' <dromede@...il.com>,
	'Grant Likely' <grant.likely@...retlab.ca>,
	'Florian Tobias Schandinat' <FlorianSchandinat@....de>,
	'Richard Purdie' <rpurdie@...ys.net>,
	linux-arm-kernel@...ts.infradead.org,
	'Jingoo Han' <jg1.han@...sung.com>
Subject: Re: [PATCH v3] backlight: corgi_lcd: Use gpio_set_value_cansleep() to
 avoid WARN_ON

On Wednesday, December 05, 2012 7:58 AM, Andrew Morton wrote
> On Tue, 04 Dec 2012 14:28:15 +0900
> Jingoo Han <jg1.han@...sung.com> wrote:
> 
> > From: Marko Katic <dromede@...il.com>
> >
> > Changing backlight intensity on an Akita (Sharp Zaurus C-1000)
> > triggers WARN_ON message:
> 
> Well, I queued it up.
> 
> > ...
> >
> > --- a/drivers/video/backlight/corgi_lcd.c
> > +++ b/drivers/video/backlight/corgi_lcd.c
> > @@ -408,11 +408,20 @@ static int corgi_bl_set_intensity(struct corgi_lcd *lcd, int intensity)
> >  	/* Bit 5 via GPIO_BACKLIGHT_CONT */
> >  	cont = !!(intensity & 0x20) ^ lcd->gpio_backlight_cont_inverted;
> >
> > -	if (gpio_is_valid(lcd->gpio_backlight_cont))
> > -		gpio_set_value(lcd->gpio_backlight_cont, cont);
> > +	if (gpio_is_valid(lcd->gpio_backlight_cont)) {
> > +		if (gpio_cansleep(lcd->gpio_backlight_cont))
> > +			gpio_set_value_cansleep(lcd->gpio_backlight_cont, cont);
> > +		else
> > +			gpio_set_value(lcd->gpio_backlight_cont, cont);
> > +	}
> 
> But this looks utterly daft.  Grant, these two things are the same - do
> we need both of them?

Hi Andrew,

There is another difference, except for warning message.
There is might_sleep_if(extra_checks) in gpio_set_value_cansleep().

Also, I saw the Documentation/gpio.txt as below:

172         /* GPIO OUTPUT */
173         void gpio_set_value(unsigned gpio, int value);
...
213         /* GPIO OUTPUT, might sleep */
214         void gpio_set_value_cansleep(unsigned gpio, int value);


Best regards,
Jingoo Han


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