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Date: Thu, 8 Sep 2011 18:35:44 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: David Daney <david.daney@cavium.com>
Cc: linux-kernel@vger.kernel.org, Richard Purdie <rpurdie@rpsys.net>,
        Trent Piepho <xyzzy@speakeasy.org>,
        Grant Likely <grant.likely@secretlab.ca>
Subject: Re: [PATCH] leds/of: leds-gpio.c: Use gpio_get_value_cansleep()
 when initializing.
Message-Id: <20110908183544.414f3add.akpm@linux-foundation.org>
In-Reply-To: <1314747592-20975-1-git-send-email-david.daney@cavium.com>
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On Tue, 30 Aug 2011 16:39:52 -0700 David Daney <david.daney@cavium.com> wrote:

> I get the following warning:
> 
> ------------[ cut here ]------------
> WARNING: at drivers/gpio/gpiolib.c:1559 __gpio_get_value+0x90/0x98()
> Modules linked in:
> Call Trace:
> [<ffffffff81440950>] dump_stack+0x8/0x34
> [<ffffffff81141478>] warn_slowpath_common+0x78/0xa0
> [<ffffffff812f0958>] __gpio_get_value+0x90/0x98
> [<ffffffff81434f04>] create_gpio_led+0xdc/0x194
> [<ffffffff8143524c>] gpio_led_probe+0x290/0x36c
> [<ffffffff8130e8b0>] driver_probe_device+0x78/0x1b0
> [<ffffffff8130eaa8>] __driver_attach+0xc0/0xc8
> [<ffffffff8130d7ac>] bus_for_each_dev+0x64/0xb0
> [<ffffffff8130e130>] bus_add_driver+0x1c8/0x2a8
> [<ffffffff8130f100>] driver_register+0x90/0x180
> [<ffffffff81100438>] do_one_initcall+0x38/0x160
> 
> ---[ end trace ee38723fbefcd65c ]---
> 
> My GPIOs are on an I2C port expander, so we must use the *_cansleep()
> variant of the GPIO functions.  This is was not being done in
> create_gpio_led().
> 
> We can change gpio_get_value() to gpio_get_value_cansleep() because it
> is only called from the platform_driver probe function, which is a
> context where we can sleep.
> 
> Only tested on my gpio_cansleep() system, but it seems safe for all
> systems.
>
> ...
>
> --- a/drivers/leds/leds-gpio.c
> +++ b/drivers/leds/leds-gpio.c
> @@ -121,7 +121,7 @@ static int __devinit create_gpio_led(const struct gpio_led *template,
>  	}
>  	led_dat->cdev.brightness_set = gpio_led_set;
>  	if (template->default_state == LEDS_GPIO_DEFSTATE_KEEP)
> -		state = !!gpio_get_value(led_dat->gpio) ^ led_dat->active_low;
> +		state = !!gpio_get_value_cansleep(led_dat->gpio) ^ led_dat->active_low;
>  	else
>  		state = (template->default_state == LEDS_GPIO_DEFSTATE_ON);
>  	led_dat->cdev.brightness = state ? LED_FULL : LED_OFF;

gpio_get_value() is an architecture-specific function whereas
gpio_get_value_cansleep() is not.  Hence all architectures will now be
forced to use the same code.  Why is this OK?

Asides:

The duplication of code between __gpio_get_value() and
gpio_get_value_cansleep() is daft.

The comment over gpio_get_value_cansleep() sucks mud rocks.