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From: Alexandre Courbot <gnurou@gmail.com>
Date: Wed, 17 Dec 2014 11:52:58 +0900
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Subject: Re: [PATCH v5 1/3] gpio: Cygnus: define Broadcom Cygnus GPIO binding
To: Arnd Bergmann <arnd@arndb.de>
Cc: "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        Ray Jui <rjui@broadcom.com>, Mark Rutland <mark.rutland@arm.com>,
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        Grant Likely <grant.likely@linaro.org>
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On Tue, Dec 16, 2014 at 6:57 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Monday 15 December 2014 13:35:47 Ray Jui wrote:
>>
>> Like I said previously, dynamic GPIO allocation works fine in the
>> kernel, as long as all of our GPIO clients in the kernel use gpiod based
>> API, which is what we will enforce going forward. The only problem is
>> with some of our customers who use GPIO through sysfs and expect fixed
>> global GPIO numbers. Thinking about this more, it's probably not that
>> difficult to add a script for those customers to convert/map the GPIO
>> numbers based on readings parsed from sysfs, so I guess that's fine.
>>
>
> I think we discussed the user space interface a number of times
> in the past, but I forgot the outcome. Either there is already
> a way to name gpio lines uniquely in sysfs, or there should be
> one.
>
> Can you reach the gpio interfaces using /sys/devices/0001234.bus/1234566.gpiocontroller/...?

No, but it seems like this is exactly the solution we need. We could
have an "export" node there that takes a relative GPIO number and
exports it under
/sys/devices/0001234.bus/1234566.gpiocontroller/exported/ the same way
the current sysfs exporter does. Then for convenience we could also
allow exported GPIOs to take names to be used under the shorter
/sys/class/gpio/ (named GPIOs is another request we pushed back many
times but that keeps coming).

Let's see if I can come with a patch. That would at least give us
something to reply to the many people that hit this issue.
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