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

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Message-ID: <CAMjpGUe9abPsdWbum2MRzOV2b5_2FDqXZC-K0KThRA6MNTr4FA@mail.gmail.com>
Date:	Sat, 22 Oct 2011 13:44:18 -0400
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	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 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.
-mike
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