linux-kernel - Re: [PATCH 2/4] powerpc/qe: new call to revert a gpio to a dedicated function

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Message-Id: <200809241155.00814.david-b@pacbell.net>
Date:	Wed, 24 Sep 2008 11:54:59 -0700
From:	David Brownell <david-b@...bell.net>
To:	avorontsov@...mvista.com
Cc:	Kumar Gala <galak@...nel.crashing.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <greg@...ah.com>,
	Timur Tabi <timur@...escale.com>,
	Li Yang <leoli@...escale.com>,
	Laurent Pinchart <laurentp@...-semaphore.com>,
	linuxppc-dev@...abs.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] powerpc/qe: new call to revert a gpio to a dedicated function

On Wednesday 24 September 2008, Anton Vorontsov wrote:
> > what do you mean by dedicated function.. be a bit clearer in the commit 
> > log.
> 
> This term is from the QE spec, I didn't invent anything. ;-)
> 
> "Each pin in the I/O ports can be configured as a general-purpose
> I/O signal or as a dedicated peripheral interface signal. ...many
> dedicated peripheral functions are multiplexed onto the ports."

Which, to me, highlights the point I've made previously:  the
right abstraction for you to work with is "pin", not GPIO.

You need to switch a QE "pin" from one of its roles to the other.

Evil things, like oopsing, will happen if you try to use this call
on a GPIO that's not backed by a QE pin.

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