| Message ID | 20210424143935.69487-1-andriy.shevchenko@linux.intel.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v1,1/1] Documentation: firmware-guide: gpio-properties: Add note to SPI CS case | expand |
On Sat, Apr 24, 2021 at 4:39 PM Andy Shevchenko <andriy.shevchenko@linux.intel.com> 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@linux.intel.com> > --- > 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!
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 ==========================
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@linux.intel.com> --- Documentation/firmware-guide/acpi/gpio-properties.rst | 6 ++++++ 1 file changed, 6 insertions(+)