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

Bartosz Golaszewski
2020-09-29T15:48:01Z

On Tue, Sep 29, 2020 at 5:43 PM Flavio Suligoi <f.suligoi@asem.it> wrote:
>
> 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

Adding Andy who knows ACPI GPIO well.

In general, the "gpio-line-names" property is used for that and it's
supported both for device tree as well as ACPI, although I have only
ever used the former.

Bartosz