linux-kernel - Re: [PATCH 1/2] drivers: create a pinmux subsystem v3

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Date:	Fri, 19 Aug 2011 13:59:00 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-kernel@...r.kernel.org,
	Martin Persson <martin.persson@...ricsson.com>,
	Joe Perches <joe@...ches.com>,
	Russell King <linux@....linux.org.uk>,
	Linaro Dev <linaro-dev@...ts.linaro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] drivers: create a pinmux subsystem v3

On Sat, Jul 9, 2011 at 12:23 PM, Mark Brown
<broonie@...nsource.wolfsonmicro.com> wrote:
> On Mon, Jun 13, 2011 at 01:57:36PM -0600, Grant Likely wrote:
>> On Mon, Jun 13, 2011 at 10:58 AM, Linus Walleij
>>
>> I would *strongly* recommend against individual device drivers
>> accessing the pinmux api.  This is system level configuration code,
>> and should be handled at the system level.
>
> There can also be advantages to putting the pin into the designed mode
> without the driver being loaded from the electrical point of view.  For
> example, selecting appropriate pull values for pads can cut down on
> power consumption.

Since the pin control subsystem is reference counting wrt
mux settings, one does not exclude the other. So for
example a driver may or may not grab a certain set-up of pins
and the core platform may do the same, but when they start to
request different conflicting things the subsystem will complain,
as is apropriate.

So this is a very pure driver framework, without policy, it just
does what it's told, and will prevent undefined and impossible
settings. Atleast that's the idea.

Thanks,
Linus Walleij
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