[v1,1/1] Documentation: firmware-guide: gpio-properties: Add note to SPI CS case

Message ID 20210424143935.69487-1-andriy.shevchenko@linux.intel.com
State New
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  • [v1,1/1] Documentation: firmware-guide: gpio-properties: Add note to SPI CS case
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Commit Message

Andy Shevchenko April 24, 2021, 2:39 p.m.
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(+)

Comments

Rafael J. Wysocki April 28, 2021, 5:12 p.m. | #1
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!

Patch

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
 ==========================