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

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Date:   Wed, 30 Sep 2020 12:04:43 +0000
From:   Flavio Suligoi <f.suligoi@...m.it>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Bartosz Golaszewski <brgl@...ev.pl>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "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 ...

Hi Andy,

> > > > > I was wondering if there is a generic GPIO driver that I can use
> Maybe I was not so clear, but as Bart mentioned the least you can do
> is simply define line name via "gpio-line-names" property. The problem
> here is when and how you would like to have them incorporated.

I already tried adding the "gpio-line-names" property, but the problem
is the same: no driver asks for this GPIO, as shown by the following
kernel messages:

ACPI: Host-directed Dynamic ACPI Table Load:
ACPI: SSDT 0xFFFF994034D42A00 0000E8 (v05 ASEMsp GPIO_BTN 00000001 INTL 20200717)
ACPI: \_SB_.GPO1.BTNS: PRP0001 requires 'compatible' property

So I'll start to write a simple device driver to use this GPIO.
I'll keep you informed!
 
> When: if ACPI tables are being provided by firmware which you may not
> alter, then you must use initramfs type of solution (no configfs,
> don't know about EFI var though). How: In that case you might have a
> chance to incorporate _DSD() method into *existing* _CRS() one.
> Possible impediments: if ACPI table from firmware already has a _DSD()
> defined or above is not working for some reason. In such a case you
> must upgrade entire DSDT via initramfs.
> 
> > > > Adding Andy who knows ACPI GPIO well.
> > >
> > > Thanks.
> > >
> > > > 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.
> > >
> > > Right. ACPI supports properties via _DSD() method.
> 
> --
> With Best Regards,
> Andy Shevchenko

Thanks Andy and Bartosz for your support!
Best regards,

Flavio