linux-kernel - Re: [PATCH v2] pinctrl: document semantics vs GPIO

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Message-ID: <CACRpkdYhy4k_JFckfYPP3ijku2O_cFQQr5810FAaje0xNr1FCw@mail.gmail.com>
Date:	Mon, 17 Sep 2012 10:58:54 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Stephen Warren <swarren@...dia.com>,
	Anmar Oueja <anmar.oueja@...aro.org>
Subject: Re: [PATCH v2] pinctrl: document semantics vs GPIO

On Fri, Sep 14, 2012 at 7:16 PM, Stephen Warren <swarren@...dotorg.org> wrote:
> On 09/14/2012 07:49 AM, Linus Walleij wrote:

>> +If a pin control driver and a GPIO driver is dealing with the same pins
>> +and the use cases involve multiplexing, you MUST implement the pin controller
>> +as a back-end for the GPIO driver like this.
>
> I might add one caveat to that:
>
> ==========
> , unless your HW design is such that the GPIO controller can override
> the pin controller's mux state, without the need for any such interaction.
> ==========

OK I buy that, so added this paragraph (slightly rephrased) and pused
for next.

> In the future, I wonder if someone might want the following caveat,
>
> ==========
> , unless you require that all boards (or device trees) define a system
> hog pinmux configuration that muxes all required GPIO signals as desired.
> ==========
>
> ... which might be appropriate for HW where GPIO-vs-special-function
> selection is performed in the pinmux controller itself, per-pin. Perhaps
> this is the OMAP special case you mentioned before?

Yeah :-/

I worry about exploding complexity here, so we need to think
about this a bit more...

Linus
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