Expose named GPIOs through sysfs

[Kevin Smith <kevin.smith@elecsyscorp.com>]

Hello,

I have several GPIOs that are not associated with kernel drivers that I 
would like to expose to userspace with names corresponding to their 
functions.  I am on Arm, so I would like to be able to specify this 
through a device tree.

As a concrete example, I have a USB device that is controlled with a 
userspace libusb driver which has a reset pin connected by GPIO.  I 
would like to expose this line as dev_reset.  Right now, userspace has 
to know the GPIO number, export the gpio, manually configure it as an 
output, then set its value.  Instead, I would like the device to simply 
show up as /sys/class/gpio/dev_reset/ (or similar) with the expected 
GPIO properties in this directory.

As a workaround, I have seen some people configure GPIOs with the LED 
driver and control the pin with "brightness", but this seems like a 
hack.  I am aware of gpio-hog, but as far as I can tell, once hogged, 
the GPIO is not exposed and cannot be changed (at least by userspace).

I see that there have been similar discussions before [1], but they 
don't seem to have reached a conclusion.  Before working on something, I 
wanted to contact the list to get some direction on the right way to 
proceed.  Is a dedicated driver the right way to do this?  Or an option 
added to the GPIO system?  I see some proposals in [2] ... is 
implementing the suggestions there the best way?

Thank you,
Kevin Smith

[1] https://www.mail-archive.com/linux-gpio@vger.kernel.org/msg00864.html
[2] https://www.mail-archive.com/linux-gpio@vger.kernel.org/msg01084.html