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

[Ricardo Ribalda <ribalda@google.com>]

On Thu, Oct 29, 2020 at 7:13 PM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
>
> On Thu, Oct 29, 2020 at 8:10 PM Ricardo Ribalda <ribalda@google.com> wrote:
> > On Thu, Oct 29, 2020 at 6:32 PM Ricardo Ribalda <ribalda@google.com> wrote:
> > > 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.
> > >
> > And there are also other devices where the swith works the other way
> > around, so the acpi should be verbose enough to describe both
> > situations.
> >
> > With my proposal (use the same active_low field as with GpioIO) we
> > cover both usecases.
>
> Even without your proposal it's feasible.
> You see, the problem here is that if you describe GPIO as Interrupt,
> the edge and level together make complete nonsense.
>
> Solution: do *not* describe it as Interrupt.

Now I get my mistake:

I thought that gpiod_to_irq will not work unless it was a GpioInt()
but it works fine. So in this case I will just convert it to that.

Could we say that doing gpiod_get_value() from a GpioInt() is always
wrong? Can we modify the code to avoid it?

Sorry for the confusion and thanks for your help.


>
> > > > [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