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

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Date:	Mon, 24 Oct 2011 09:26:38 +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 Sat, Oct 22, 2011 at 7:44 PM, Mike Frysinger <vapier.adi@...il.com> wrote:
> On Tue, Oct 4, 2011 at 16:35, Grant Likely wrote:
>> On Sat, Oct 01, 2011 at 12:39:21PM +0200, Linus Walleij wrote:
>>> 2011/9/30 Grant Likely:
>>> > I'm not convinced that the sysfs approach is
>>> > actually the right interface here (I'm certainly not a fan of the gpio
>>> > sysfs i/f), and I'd rather not be putting in unneeded stuff until the
>>> > userspace i/f is hammered out.
>>>
>>> Actually, thinking about it I cannot see what would be wrong
>>> with /dev/gpio0 & friends in the first place.
>>>
>>> Using sysfs as swiss army knife for custom I/O does not
>>> seem like it would be long-term viable so thanks for this
>>> observation, and I think we need /dev/gpio* put on some
>>> mental roadmap somewhere.
>>
>> Agreed.  I don't want to be in the situation we are now with GPIO,
>> where every time I look at the sysfs interface I shudder.
>
> the problem with that is it doesn't scale.  if i have a device with
> over 150 GPIOs on the SoC itself (obviously GPIO expanders can make
> that much bigger), i don't want to see 150+ device nodes in /dev/.
> that's a pretty big waste.  sysfs only allocates/frees resources when
> userspace actually wants to utilize a GPIO.

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.

Yours,
Linus Walleij
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