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

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

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?

-- 
With Best Regards,
Andy Shevchenko