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

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Message-ID: <20111024110518.GG8708@ponder.secretlab.ca>
Date:	Mon, 24 Oct 2011 13:05:18 +0200
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Mike Frysinger <vapier.adi@...il.com>,
	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 09:48:19AM +0200, Linus Walleij wrote:
> On Mon, Oct 24, 2011 at 9:36 AM, Grant Likely <grant.likely@...retlab.ca> wrote:
> > On Mon, Oct 24, 2011 at 09:26:38AM +0200, Linus Walleij wrote:
> (...)
> >> I was more thinking along the lines of one device per GPIO controller,
> >> then you ioctl() to ask /dev/gpio0 how many pins it has or so.
> >
> > And there is also the question of whether it is even a good idea to
> > export pinctrl manipulation to userspace.
> 
> The application I've seen is in automatic control.
> 
> I think people do things like connect they GPIO pins to electrical
> relays, plus on top of that they use all the stuff in drivers/staging/iio.
> 
> All that from userspace. Controlling entire factories and industrial
> robots, weapon systems too, I'm afraid.
> 
> The control of these dangerous things runs on a realtime-patched
> kernel, in a single userspace app with a few threads and they have
> done some realtime-tetris scheduling the beast more or less
> manually with SCHED_FIFO. Basically that app is all that runs on
> the board, and its threads take precedence over everything else
> on the system.
> 
> That is the typical beast that is poking around on the GPIO sysfs
> interfaces...

... which maybe should be encouraged to use some form of uio driver.  :-)

g.

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