Re: [PATCH v1 2/3] Documentation: firmware-guide: gpio-properties: active_low only for GpioIo()

From: Ricardo Ribalda <ribalda@google.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>
Subject: Re: [PATCH v1 2/3] Documentation: firmware-guide: gpio-properties: active_low only for GpioIo()
Date: Thu, 29 Oct 2020 18:32:46 +0100
Message-ID: <CANiDSCtNCn+vj=8kgx8oPUbCJS6mLmOckiWpJtobT_FtUCR3YQ@mail.gmail.com> (raw)
In-Reply-To: <CAHp75Vd+doPgSZQEOSAW4oRoAqPUdJyoivtNvbO5d1q-e280Eg@mail.gmail.com>

Hi Andy

On Thu, Oct 29, 2020 at 6:26 PM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
>
> On Thu, Oct 29, 2020 at 7:20 PM Andy Shevchenko
> <andy.shevchenko@gmail.com> wrote:
> >
> > On Thu, Oct 29, 2020 at 7:17 PM Andy Shevchenko
> > <andy.shevchenko@gmail.com> wrote:
> > > On Thu, Oct 29, 2020 at 4:55 PM Ricardo Ribalda <ribalda@google.com> wrote:
> > > > On Thu, Oct 29, 2020 at 3:45 PM Andy Shevchenko
> > > > <andriy.shevchenko@linux.intel.com> wrote:
> > > > > On Wed, Oct 28, 2020 at 10:10:42PM +0100, Ricardo Ribalda wrote:
> > >
> > > ...
> > >
> > > > > ActiveLevel field is described in 19.6.55 GpioInt (GPIO Interrupt Connection
> > > > > Resource Descriptor Macro).
> > > > >
> > > > > > Without using the active_low, how can we describe  a pin that is
> > > > > > active low and has to trigger an irq on both edges?
> > > > >
> > > > > This is nonsense.
> > > > > What does it mean?
> > > >
> > > > Let me try to explain myself again:
> > > >
> > > > I have a gpio pin that produces IRQs on both edges. so ActiveLevel is Both
> > > >
> > > > The problem is that the value of that pin is inverted: Low means 1 and
> > > > high means 0.
> > > >
> > > > How can I describe that the pin "is inverted" without using the _DSD field?
> > >
> > > "Both edges" and "inverted" or "polarity low" in one sentence make no sense.
> >
> > To be on the constructive side, I can *imagine* so badly designed
> > hardware that uses level and edge at the same time, but before I go to
> > conclusions, can you share relevant (pieces of) datasheet?
>
> The [1] is a real example of how GPIO is being used to detect changing
> of current level of the signal.
> Note, ACPI tables for that device have problems [2], but I guess you
> may get the idea.

This is exactly what I need to do. Get an IRQ whenever the value
changes. But the pin is "inverted"

This is the "schematic" :  https://ibb.co/f8GMBbP . I want to pass to
userspace a "1" when the switch is closed and "0"  when it is open.

>
>
> [1]: https://elixir.bootlin.com/linux/latest/source/drivers/extcon/extcon-intel-int3496.c#L138
> [2]: https://elixir.bootlin.com/linux/latest/source/drivers/extcon/extcon-intel-int3496.c#L45
>
> --
> With Best Regards,
> Andy Shevchenko

-- 
Ricardo Ribalda