linux-kernel - Re: [PATCH v4] backlight: corgi_lcd: Use gpio_set_value_cansleep() to avoid WARN

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Date:	Wed, 5 Dec 2012 09:30:27 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Jingoo Han <jg1.han@...sung.com>
Cc:	'Andrew Morton' <akpm@...ux-foundation.org>,
	'LKML' <linux-kernel@...r.kernel.org>,
	'Florian Tobias Schandinat' <FlorianSchandinat@....de>,
	'Marko Katic' <dromede@...il.com>,
	'Grant Likely' <grant.likely@...retlab.ca>,
	'Richard Purdie' <rpurdie@...ys.net>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4] backlight: corgi_lcd: Use gpio_set_value_cansleep()
	to avoid WARN_ON

On Wed, Dec 05, 2012 at 09:59:07AM +0900, Jingoo Han wrote:
> -	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);
> +	}

Why not simply:

+	if (gpio_is_valid(lcd->gpio_backlight_cont))
+		gpio_set_value_cansleep(lcd->gpio_backlight_cont, cont);

If you read the gpiolib code and documentation, what you will realise is
that the two calls are identical except for the "might_sleep_if()" in
gpio_set_value_cansleep().  You will also note that gpiolib itself _only_
calls gpio_set_value_cansleep() without checking gpio_cansleep() in
contexts where sleeping is possible.  So if it's good enough for gpiolib,
it should be good enough here.
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