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

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Date:   Tue, 29 Sep 2020 17:47:48 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Flavio Suligoi <f.suligoi@...m.it>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: How to use an ACPI declared GPIO in a userspace ...

On Tue, Sep 29, 2020 at 5:43 PM Flavio Suligoi <f.suligoi@...m.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