On Tue, Dec 16, 2014 at 6:57 AM, Arnd Bergmann [off-list ref] wrote:

On Monday 15 December 2014 13:35:47 Ray Jui wrote:

quoted

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.