Messages in this thread Patch in this message | | | From | Andy Shevchenko <> | Subject | [PATCH v1 1/1] Documentation: firmware-guide: gpio-properties: Add note to SPI CS case | Date | Sat, 24 Apr 2021 17:39:35 +0300 |
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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 ========================== -- 2.30.2
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