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

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Message-ID: <20200930130113.GQ3956970@smile.fi.intel.com>
Date:   Wed, 30 Sep 2020 16:01:13 +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 Wed, Sep 30, 2020 at 12:04:43PM +0000, Flavio Suligoi wrote:
> > > > > > 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.

I guess you simply didn't get. The "gpio-line-names" property of GPIO
*controller* (provider!) and you are trying to do something with the *consumer*
if I got it right.

And of course GPIO line, which has name, has no difference in use from another
w/o name assigned. You will need to request it by *consumer* either in kernel
or in user space.

To be more precise we have to look at your DSDT.

-- 
With Best Regards,
Andy Shevchenko