How to use an ACPI declared GPIO in a userspace ...

[Flavio Suligoi <f.suligoi@asem.it>]

Hi all,

I need to expose to the userspace a GPIO, physically connected to a board
push-button. This GPIO must expose a pre-defined name, such as
"user-push-button", so that the userspace applications can use it without
know any physical GPIO details.

I can customize the board BIOS and so my goal is to add an ACPI table with
a content like this:

...
Scope (\_SB.GPO1)
	{
		Device (BTNS)
		{
			Name (_HID, "PRP0001")
			Name (_DDN, "GPIO buttons device")

			Name (_CRS, ResourceTemplate ()
			{
				GpioIo (
				Exclusive,               // Not shared
				PullNone,                // No need for pulls
				0,                       // Debounce timeout
				0,                       // Drive strength
				IoRestrictionInputOnly,  // Only used as input
				"\\_SB.GPO1",            // GPIO controller
				0, ResourceConsumer, , ) // Must be 0
				{
					25,              // GPIO number
				}
...

I know that this GPIO can be used from other drivers.
For example I successfully tested it using the "gpio-keys" device driver,
giving to my GPIO a key-code and emulating in this way a keyboard key.
This could be a possible solution.

But I prefer to expose my GPIO as a classic GPIO, not as a keyboard key.

I was wondering if there is a generic GPIO driver that I can use to expose
this GPIO with its pre-defined name (caming from the ACPI table declaration),
to the userspace...

Best regards,

Flavio