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

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Date:	Fri, 14 Sep 2012 15:48:05 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>,
	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>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] pinctrl: document semantics vs GPIO

On Fri, Sep 14, 2012 at 12:11 AM, Domenico Andreoli <cavokz@...il.com> wrote:
> On Thu, Sep 13, 2012 at 10:11:29AM -0600, Stephen Warren wrote:

>> I think it makes sense to more strongly recommend that for GPIO muxing,
>> the GPIO driver always call into the pinctrl subsystem (if needed by the
>> HW) to perform that muxing, so that standalone gpio_direction_*() always
>> work without any use of pinctrl; the interaction between the two should
>> only be required if pin configuration (not just pin muxing) is also
>> required.
>
> Don't know. Isn't possible to reach the same effect moving this kind
> of knowledge into higher level helper functions and remove this bridge
> across the subsystems?

I'm not following, please elaborate on this.

What are these higher level functions, and where will they be
located? In which subsystem, and using what symbols/signatures and
so on?

Deepak or Arnd suggested to add a set of functions to the pinctrl
driver vtable and make it possible to implement a generic gpio_chip
deeply merged with a pin controller driver. I'm considering this,
since it would also be a natural stepping stone to the /dev/pinctrl0
device(s) I want to see for userspace access the day we need it.

> Because there is also the pin config stuff that
> may require special mixing as well and it's clear that there is no space
> for it in these calls.

Yes but it is clear from the above that this need to be handled by
pin control, either through hogs or as a last resort at runtime
in the driver.

Yours,
Linus Walleij
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