linux-kernel - Re: [PATCH v2] pinctrl: elaborate a bit on arrangements in doc

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Date:	Wed, 3 Jul 2013 10:54:04 +0200
From:	Christian Ruppert <christian.ruppert@...lis.com>
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>,
	Tony Lindgren <tony@...mide.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Rob Landley <rob@...dley.net>
Subject: Re: [PATCH v2] pinctrl: elaborate a bit on arrangements in doc

On Thu, Jun 27, 2013 at 04:00:49PM -0600, Stephen Warren wrote:
> On 06/27/2013 03:54 AM, Linus Walleij wrote:
> > From: Linus Walleij <linus.walleij@...aro.org>
> [...]
> > +From a kernel point of view, however, these are different aspects of the
> > +hardware and shall be put into different subsystems.
> > +
> > +Electrical properties of the pin such as biasing and drive strength
> > +may be placed at some pin-specific register in all cases or as part
> > +of the GPIO register in case (B) especially. This doesn't mean that such
> > +properties necessarily pertain to what the Linux kernel calls "GPIO".
> 
> Is it worth explaining which Linux subsystem each of the three aspects
> are controlled by. Something like:
> 
> -----
> Registers (or fields within registers) that control electrical
> properties of the pin such as biasing and drive strength should be
> exposed through the pinctrl subsystem, as "pin configuration" settings.
> 
> Registers (or fields within registers) that control muxing of signals
> from various other HW blocks (e.g. I2C, MMC, or GPIO) onto pins should
> be exposed through the pinctrl subssytem, as mux functions.
> 
> Registers (or fields within registers) that control GPIO functionality
> such as setting a GPIO's output value, reading a GPIO's input value, or
> setting GPIO pin direction should be exposed through the GPIO subsystem.
> 
> Depending on the exact HW register design, some functions exposed by the
> GPIO subsystem may call into the pinctrl subsystem in order to
> co-ordinate register settings across HW modules. In particular, this may
> be needed for HW with separate GPIO and pin controller HW modules, where
> e.g. GPIO direction is determined by a register in the pin controller HW
> module rather than the GPIO HW module.
> -----

I agree, this is really worth mentioning in some place, maybe even a
more prominent one than here.

-- 
  Christian Ruppert              ,          <christian.ruppert@...lis.com>
                                /|
  Tel: +41/(0)22 816 19-42     //|                 3, Chemin du Pré-Fleuri
                             _// | bilis Systems   CH-1228 Plan-les-Ouates
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