linux-kernel - Re: [PATCH 1/3] gpiolib: make gpio_to

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Date:	Thu, 14 Aug 2008 19:10:22 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Laurent Pinchart <laurentp@...-semaphore.com>
Cc:	linuxppc-dev@...abs.org, Greg Kroah-Hartman <greg@...ah.com>,
	linux-usb@...r.kernel.org,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Li Yang <leoli@...escale.com>, linux-kernel@...r.kernel.org,
	Timur Tabi <timur@...escale.com>
Subject: Re: [PATCH 1/3] gpiolib: make gpio_to_chip() public

On Thu, Aug 14, 2008 at 04:45:52PM +0200, Laurent Pinchart wrote:
> On Thursday 14 August 2008, Anton Vorontsov wrote:
> > On Thu, Aug 14, 2008 at 04:04:18PM +0200, Laurent Pinchart wrote:
> > > On Friday 08 August 2008, Anton Vorontsov wrote:
> > > > We'll need this function to write platform-specific hooks to deal
> > > > with pin's dedicated functions. Quite obviously this will work only
> > > > for the platforms with 1-to-1 GPIO to PIN mapping.
> > > > 
> > > > This is stopgap solution till we think out and implement a proper
> > > > api (pinlib?).
> > > 
> > > How do you support reverting the GPIO mode to non-dedicated ?
> > 
> > As we always do with the GPIO API: gpio_direction_*() calls.
> 
> So the proper sequence to configure a pin in dedicated mode is to set
> the direction first (which will unset the dedicated mode bit) and
> then set dedicated mode (which will not touch the direction bit) ?

Not exactly. But you can do this way, if you need to preserve
a direction. What I did is a bit different though.

qe_gpio_set_dedicated() actually just restores a mode that
firmware had set up, including direction (since direction could
be a part of dedicated configuration).

That is, upon GPIO controller registration, we save all registers,
then driver can set up a pin to a GPIO mode via standard API, and
then it can _revert_ a pin to a dedicated function via
qe_gpio_set_dedicated() call. Dedicated function is specified by
the firmware (or board file), we're just restoring it.

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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