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

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Message-ID: <CAHp75Vfh7u+va0CVCQxSe7unk8qGiWnNrpKHXVH3fKBYzqEUVA@mail.gmail.com>
Date:   Fri, 2 Oct 2020 15:40:13 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Flavio Suligoi <f.suligoi@...m.it>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        "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 Fri, Oct 2, 2020 at 1:26 PM Flavio Suligoi <f.suligoi@...m.it> wrote:
> Hi Andy,
>
> with my custom SSDT table:
>
> DefinitionBlock ("gpio_button.aml", "SSDT", 5, "ASEMsp", "GPIO_BTN", 1)
> {
>         External (_SB_.GPO1, DeviceObj)
>         Scope (\_SB.GPO1)
>         {
>                 Device (BTNS)
>                 {
>                         Name (_HID, "ASEM0005")         // _HID: Hardware ID PRP0001
>                         Name (_UID, Zero)             // _UID: Unique ID
>                         Name (_DDN, "DDN - SW Readable Button")  // _DDN: DOS Device Name
>                         Name (_STR, Unicode ("STR - SW Readable Button"))  // _STR: Description String
>
>                         Name (_CRS, ResourceTemplate ()  // _CRS: Current Resource Settings
>                         {
>                                 GpioIo (
>                                         Shared,                  // 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 25
>                                         }
>                         })
>                 }
>         }
> }
>
> I'm able to see the GPIO in:
>
> /sys/bus/platform/devices/ASEM0005:00/firmware_node:
>
> -r--r--r--    1 root     root          4096 Oct  2 12:10 description
> -r--r--r--    1 root     root          4096 Oct  2 12:10 hid
> -r--r--r--    1 root     root          4096 Oct  2 12:10 modalias
> -r--r--r--    1 root     root          4096 Oct  2 12:10 path
> lrwxrwxrwx    1 root     root             0 Oct  2 12:10 physical_node -> ../../../../platform/INT3452:01/ASEM0005:00
> drwxr-xr-x    2 root     root             0 Oct  2 12:10 power
> lrwxrwxrwx    1 root     root             0 Oct  2 12:10 subsystem -> ../../../../../bus/acpi
> -rw-r--r--    1 root     root          4096 Oct  2 12:10 uevent
> -r--r--r--    1 root     root          4096 Oct  2 12:10 uid
>
> and so I can see some useful info:
>
> # cat description
> STR - SW Readable Button
> # cat hid
> ASEM0005
> # cat modalias
> acpi:ASEM0005:
> bmxxxx-x86-64:/sys/bus/platform/devices/ASEM0005:00/firmware_node# cat path
> \_SB_.GPO1.BTNS
>
> So, from userspace, I can discover the GPIO controller /dev/gpiochip1,
> but I don't know how to discover the GPIO number (25 in this case).
> Do you have any suggestion about how to discover this GPIO number?

You don't need this SSDT at all.

-- 
With Best Regards,
Andy Shevchenko