linux-kernel - Re: [PATCH v2 1/4] gpiolib: Add "unknown" direction support

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Date:	Thu, 17 Feb 2011 12:05:47 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Eric Miao <eric.y.miao@...il.com>
Cc:	Peter Tyser <ptyser@...-inc.com>, linux-kernel@...r.kernel.org,
	Alek Du <alek.du@...el.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	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 v2 1/4] gpiolib: Add "unknown" direction support

On Thu, Feb 17, 2011 at 03:33:42PM +0800, Eric Miao wrote:
> On Thu, Feb 17, 2011 at 8:56 AM, Peter Tyser <ptyser@...-inc.com> 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.
> >
> 
> Hrm... that's why I don't like the original definition of gpio_request()
> which is vague on the pin configurations. The pin configuration should
> be clear upon requesting, otherwise it's a potential issue.
I don't know (state: "unknown" :-) what you would prefer here.  An
implicit gpio_direction_input()?  Or gpio_reserve_and_direction_input()?

Best regards
Uwe

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