On Sat, Apr 24, 2021 at 4:39 PM Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote: > > Historically ACPI has no means of the GPIO polarity and thus > the SPISerialBus() resource defines it on the per-chip basis. > In order to avoid an ambiguity, the GPIO polarity is considered > being always Active High. > > Add note about this to the respective documentation file. > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > --- > Documentation/firmware-guide/acpi/gpio-properties.rst | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/Documentation/firmware-guide/acpi/gpio-properties.rst b/Documentation/firmware-guide/acpi/gpio-properties.rst > index 4e264c16ddff..df4b711053ee 100644 > --- a/Documentation/firmware-guide/acpi/gpio-properties.rst > +++ b/Documentation/firmware-guide/acpi/gpio-properties.rst > @@ -99,6 +99,12 @@ native:: > } > } > > +Note, that historically ACPI has no means of the GPIO polarity and thus > +the SPISerialBus() resource defines it on the per-chip basis. In order > +to avoid a chain of negations, the GPIO polarity is considered being > +Active High. Even for the cases when _DSD() is involved (see the example > +above) the GPIO CS polarity must be defined Active High to avoid ambiguity. > + > Other supported properties > ========================== > > -- Applied as 5.13-rc material, thanks!
