linux-kernel - RE: [RFC PATCH] Rework gpio cansleep (was Re: gpiolib and sleepinggpios)

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Date:	Thu, 24 Jun 2010 05:46:11 +0100
From:	Jon Povey <Jon.Povey@...elogic.co.uk>
To:	Ryan Mallon <ryan@...ewatersys.com>,
	David Brownell <david-b@...bell.net>
CC:	David Brownell <dbrownell@...rs.sourceforge.net>,
	"gregkh@...e.de" <gregkh@...e.de>,
	linux kernel <linux-kernel@...r.kernel.org>,
	"ext-jani.1.nikula@...ia.com" <ext-jani.1.nikula@...ia.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [RFC PATCH] Rework gpio cansleep (was Re: gpiolib and
 sleepinggpios)

Ryan Mallon wrote:

> If we strip my patch back to just introducing gpio_request_cansleep,
> which would be used in any driver where all of the calls are
> gpio_(set/get)_cansleep, and make gpio_request only allow non-sleeping
> gpios then incorrect use of gpios would be caught at request time and
> returned to the caller as an error.

It seems like a good idea to catch these at request time. There is support in the API for this already (gpio_cansleep), but driver writers are not steered towards checking and thinking in these ways by the current API or documentation. Perhaps a documentation change with some cut and paste boilerplate would be enough, but I think some API enforcement/encouragement would be helpful.

I think this agrees with you, Ryan:

gpio_request_cansleep would be the same as current gpio_request
gpio_request changes to error if this is a sleepy gpio.

Imagine a situation where GPIOs are being assigned and passed around between drivers in some dynamic way, or some way unpredictable to the driver writer. In development only non-sleeping GPIOs have been seen and everything is fine. One day someone feeds it a GPIO on an I2C expander and the driver crashes.
If gpio_request had this built-in check the driver could gracefuly fail to load instead with an appropriate error message.

--
Jon Povey
jon.povey@...elogic.co.uk

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