linux-kernel - Re: [RFC PATCH v2 00/13] arm/tegra: Initialize GPIO & pinmux from DT

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Date:	Wed, 17 Aug 2011 13:23:38 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Stephen Warren <swarren@...dia.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Colin Cross <ccross@...roid.com>,
	Erik Gilling <konkers@...roid.com>,
	Olof Johansson <olof@...om.net>,
	Russell King <linux@....linux.org.uk>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Belisko Marek <marek.belisko@...il.com>,
	Jamie Iles <jamie@...ieiles.com>,
	Shawn Guo <shawn.guo@...escale.com>,
	Sergei Shtylyov <sshtylyov@...sta.com>
Subject: Re: [RFC PATCH v2 00/13] arm/tegra: Initialize GPIO & pinmux from DT

On Tuesday 16 August 2011, Stephen Warren wrote:
> One issue here: There isn't always a single gpio/pinmux parent; as a
> concrete example, the ALSA/ASoC driver for Tegra+WM8903 uses GPIOs both
> from Tegra itself, and from the WM8903 audio codec.
> 
> I could imagine the same being true in basically any case where one
> device uses N GPIOs (e.g. SD controller with power, change-detect,
> and read-only GPIOs; some could easily come from the SoC and some
> from a GPIO expander).
> 
> I'm not quite so sure that multiple parents would be useful for pinmux,
> but I wouldn't say that it was impossible...

Hmm, how common do you think the example is?

It it's just a very rare case, we can still special-case it by
introducing fake subdevices for the Tegra+WM8903 driver, each of
which has only one gpio-parent. This is ugly but keeps the special
case to the rare devices.

If we can expect more than a handful of these, we probably need
a better design for the binding, which will cause a burden for
all drivers.

	Arnd
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