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

[Ricardo Ribalda <ribalda@google.com>]

Hi Andy

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:
> > Hi Andy
> >
> > Thanks for your patch and super fast response.
> >
> > I think there are two different concepts here:
> >
> > 1) when the pin has a low value, it is  0 or a 1? =>active_low
>
> I'm not sure I have got it. GpioIo() has no such property and
> _DSD active_low is documented as being polarity setting:
>
>         active_low == 1 => active low polarity.
>
> > 2) when do I get an irq, low->high or high->low => irq polarity
>
> IRQ polarity is clearly defined by GpioInt() resource in the ACPI
> specification.
>
> > When I read the acpi spec for GpioInt()
> > https://www.uefi.org/sites/default/files/resources/ACPI_6_2.pdf page
> > 934, it has the same problem as for GpioIo(), it does not express the
> > active_low and this is where the _DSD field comes handy.
>
> 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?

Best regards

>
> --
> With Best Regards,
> Andy Shevchenko
>
>


-- 
Ricardo Ribalda