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

[Ricardo Ribalda <ribalda@xxxxxxxxxxxx>]

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

2) when do I get an irq, low->high or high->low => irq polarity

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.

Without using the active_low, how can we describe  a pin that is
active low and has to trigger an irq on both edges?

Thanks again


On Wed, Oct 28, 2020 at 9:51 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> It appears that people may misinterpret active_low field in _DSD
> for GpioInt() resource. Add a paragraph to clarify this.
>
> Reported-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> ---
>  Documentation/firmware-guide/acpi/gpio-properties.rst | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/Documentation/firmware-guide/acpi/gpio-properties.rst b/Documentation/firmware-guide/acpi/gpio-properties.rst
> index e6e65ceb2ca1..370fe46c6af9 100644
> --- a/Documentation/firmware-guide/acpi/gpio-properties.rst
> +++ b/Documentation/firmware-guide/acpi/gpio-properties.rst
> @@ -55,6 +55,9 @@ Since ACPI GpioIo() resource does not have a field saying whether it is
>  active low or high, the "active_low" argument can be used here.  Setting
>  it to 1 marks the GPIO as active low.
>
> +Note, active_low in _DSD does not make sense for GpioInt() resource and
> +must be 0. GpioInt() resource has its own means of defining it.
> +
>  In our Bluetooth example the "reset-gpios" refers to the second GpioIo()
>  resource, second pin in that resource with the GPIO number of 31.
>
> --
> 2.28.0
>


-- 
Ricardo Ribalda