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
==========================
--
2.30.2
