linux-kernel - Re: [PATCH] drivers: create a pin control subsystem v8

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Message-ID: <CACRpkdbbNTGd3opbeAiY2uMpPzD+G_vj=jq_fiArhjosPXyMRQ@mail.gmail.com>
Date:	Mon, 24 Oct 2011 14:28:26 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.ml.walleij@...il.com>,
	Stephen Warren <swarren@...dia.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Barry Song <21cnbao@...il.com>, linux-kernel@...r.kernel.org,
	Joe Perches <joe@...ches.com>,
	Russell King <linux@....linux.org.uk>,
	Linaro Dev <linaro-dev@...ts.linaro.org>,
	Lee Jones <lee.jones@...aro.org>,
	David Brown <davidb@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org,
	Stijn Devriendt <highguy@...il.com>
Subject: Re: [PATCH] drivers: create a pin control subsystem v8

On Mon, Oct 24, 2011 at 11:20 AM, Mike Frysinger <vapier.adi@...il.com> wrote:

> but the question here is about pinctrl.  does userspace really need to
> manipulate the pinmapping ?  if we agree on that, then the question is
> on the userspace interface.
>
> assuming we want this, i can't see the performance argument being made
> here for pinctrl.  which means doing a sysfs interface here like we
> already have with GPIO makes the most sense.  GPIO deals in "binary"
> data for the most part (reading/writing 0/1 ints) so the string-based
> sysfs parsing is a bit weird, but pinctrl deals with strings
> everywhere for selecting mapping groups, so sysfs is the natural
> answer.

Hm now I feel I start to agree with you and come back to my
original proposition to do pinctrl in sysfs after all.

I wonder how soon we have a practical use case for this.
We do have this hacked-up driver in ux500:
http://git.linaro.org/gitweb?p=bsp/st-ericsson/linux-3.0-ux500.git;a=tree;f=drivers/staging/ab5500_sim;hb=HEAD

This controls a lot of SIM card pins from userspace...

Yours,
Linus Walleij
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