linux-kernel - Re: [PATCH v2] GPIO: Add gpio

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Message-ID: <20091012092331.45d7e71b@bike.lwn.net>
Date:	Mon, 12 Oct 2009 09:23:31 -0600
From:	Jonathan Corbet <corbet@....net>
To:	Ben Nizette <bn@...sdigital.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	dsilvers@...tec.co.uk
Subject: Re: [PATCH v2] GPIO: Add gpio_lookup

On Mon, 12 Oct 2009 17:11:44 +1100
Ben Nizette <bn@...sdigital.com> wrote:

> Back to this patch though, the gpio names have to come from the platform
> code via some platform_data for the gpio chip [1], the driver then looks
> up that pre-defined name to find the gpio number.  Why not just pass the
> gpio number straight to the end device driver through platform_data and
> bypass the middle-man?

That's true in a situation where you've one One Platform to Bind Them
All, yes.  But if you have (say) GPIOs provided by a PCI-connected
peripheral which are needed in (say) a camera driver, there is no one
platform which can manage all those GPIO numbers.  In particular, I've
done a driver for viafb-based GPIOs; these devices can show up in any
of a number of x86-based systems.  I honestly don't know why it would
make sense to try to hardware numbers to these GPIOs when using names
and dynamic numbering is so much more flexible - and we are already
tracking the names.

Perhaps it would make sense to implement a proper namespace layer for
GPIOs rather than continuing to grow something which evidently sneaked
in through the back door.  Until that's done, though, I think this
patch is useful.  But it it's really unwanted I'll find some other way.

Thanks,

jon
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