linux-kernel - Re: [PATCH v3 1/4] gpiolib: Add "unknown" direction support

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Date:	Fri, 18 Feb 2011 09:51:23 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Peter Tyser <ptyser@...-inc.com>
Cc:	linux-kernel@...r.kernel.org, Alek Du <alek.du@...el.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Eric Miao <eric.y.miao@...il.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Joe Perches <joe@...ches.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH v3 1/4] gpiolib: Add "unknown" direction support

Hello,

On Thu, Feb 17, 2011 at 05:03:16PM -0600, Peter Tyser wrote:
> Previously, gpiolib would unconditionally flag all GPIO pins as inputs,
> regardless of their true state.  This resulted in all GPIO output pins
> initially being incorrectly identified as "input" in the GPIO sysfs.
> 
> Since the direction of GPIOs is not known prior to having their
> direction set, instead set the default direction to "unknown" to prevent
> user confusion.  A pin with an "unknown" direction can not be written or
> read via sysfs; it must first be configured as an input or output before
> it can be used.
> 
> While we're playing with the direction flag in/out defines, rename them to
> a more descriptive FLAG_DIR_* format.
Would it make sense to reset the state to unknown on gpio_free?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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