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Date: Wed, 5 Dec 2012 09:30:27 +0000
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Jingoo Han <jg1.han@samsung.com>
Cc: "'Andrew Morton'" <akpm@linux-foundation.org>,
        "'LKML'" <linux-kernel@vger.kernel.org>,
        "'Florian Tobias Schandinat'" <FlorianSchandinat@gmx.de>,
        "'Marko Katic'" <dromede@gmail.com>,
        "'Grant Likely'" <grant.likely@secretlab.ca>,
        "'Richard Purdie'" <rpurdie@rpsys.net>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4] backlight: corgi_lcd: Use gpio_set_value_cansleep()
	to avoid WARN_ON
Message-ID: <20121205093027.GK14363@n2100.arm.linux.org.uk>
References: <000201cdd283$baf50160$30df0420$%han@samsung.com>
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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.