linux-kernel - Re: [PATCH 1/2] pinmux: Add TB10x pinmux driver

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Date:	Fri, 7 Jun 2013 15:34:50 +0200
From:	Christian Ruppert <christian.ruppert@...lis.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Haojian Zhuang <haojian.zhuang@...aro.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Shiraz HASHIM <shiraz.hashim@...com>,
	Patrice CHOTARD <patrice.chotard@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	Sascha Leuenberger <sascha.leuenberger@...lis.com>,
	Pierrick Hascoet <pierrick.hascoet@...lis.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 1/2] pinmux: Add TB10x pinmux driver

On Fri, Jun 07, 2013 at 01:36:16PM +0200, Linus Walleij wrote:
> On Mon, Jun 3, 2013 at 11:42 AM, Christian Ruppert
> <christian.ruppert@...lis.com> wrote:
> 
> > Ease of use is also the reason why I added the gpio-base property to the
> > original driver: Finding out the global GPIO number to use in
> > /sys/class/gpio for a given GPIO of a given bank seems to be a recurring
> > headache for our customers and the definition of the bank's base number
> > in the device tree is an attempt to improve this situation.
> 
> What you need to do in that case is to find a way to name the pins
> in sysfs (creating symbolic links with the GPIO pin name) so they
> can use these names in sysfs instead.
> 
> There is no ambition from my side to try to correlate the
> GPIO sysfs interface and device trees. This is because the GPIO
> sysfs is not universally liked. And when you say you want to make the
> sysfs ABI easy to use that lights a big red light on my panel. I will
> explain why.
> 
> What is very important is that your customers understand that
> the GPIO sysfs shall not be used for things like:
> 
> - LEDs
> - Switches
> - Regulators
> - Camera muxes
> - etc
> 
> From the kernel community we have tried (or atleast I have tried)
> that this kind of hardware shall be handled by the apropriate linux
> subsystems, and not by obscure userspace code.

I totally agree with that and we already declare the LEDs etc. on our
PCBs in the device trees. However, we have at least one customer who has
a user space driver for some peripheral on i2c which needs to be reset
through GPIO. I'm not sure which framework to use for this sort of
applications.

Greetings,
  Christian

-- 
  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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