linux-kernel - How to use an ACPI declared GPIO in a userspace ...

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Message-ID: <9152bb8be33e4192a7766eb53c6ca9af@asem.it>
Date:   Tue, 29 Sep 2020 15:37:46 +0000
From:   Flavio Suligoi <f.suligoi@...m.it>
To:     "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: How to use an ACPI declared GPIO in a userspace ...

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