linux-kernel - Re: [PATCH v3 2/4] gpiolib: Add ability to get GPIO pin direction

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Date:	Fri, 18 Feb 2011 14:27:23 -0600
From:	Peter Tyser <ptyser@...-inc.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
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 2/4] gpiolib: Add ability to get GPIO pin direction

On Fri, 2011-02-18 at 19:49 +0100, Uwe Kleine-König wrote:
> Hello Peter,
> 
> On Fri, Feb 18, 2011 at 11:36:26AM -0600, Peter Tyser wrote:
> > On Fri, 2011-02-18 at 09:57 +0100, Uwe Kleine-König wrote:
> > > On Thu, Feb 17, 2011 at 05:03:17PM -0600, Peter Tyser wrote:
> > > > Add a new get_direction() function to the gpio_chip structure.  This is
> > > > useful so that the direction of a pin can be determined when its
> > > > initially exported.  Previously, the direction defaulted to "unknown"
> > > > regardless of the actual configuration of the GPIO pin.
> > > > 
> > > > If a GPIO driver implements get_direction(), it is called in
> > > > gpio_request() to set the initial direction of the pin accurately.
> > > IMHO the commit log is conceptually wrong, because it talks about a
> > > "pin".  Better use gpio here.
> > 
> > I don't follow.  I used "pin" to make it clear that the get_direction()
> > function operates on a pin-by-pin basis, and to help reduce any
> > ambiguity about if a gpio chip or gpio pin is being referred to.  Would
> > you prefer that the "pin" references are clarified to be "GPIO pin"?
> Maybe it's just that we use different terms.  For me a "pin" is an
> entry/exit point into/from a cpu or other chip.  A gpio is (hmm, how
> should I say) a concept how to drive a pin.  A gpio might or might not
> be "connected" to a pin at a given time.

Ahh, I see...  The GPIO subsystem doesn't have the capability to
multiplex a GPIO to different physical pins at the moment, so I always
equate a GPIO with a specific pin, even if its not "connected" all the
time.  I'll remove the "pin" references when I resubmit if you think it
is more accurate.

Peter

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