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Documentation: firmware-guide: gpio-properties: Clarify Explicit and Implicit

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Clarify the Explicit and Implicit meanings in the table of Pull Bias.

While at it, distinguish pull bias keywords used in ACPI by using bold
font in the table of the respective terms.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Andy Shevchenko 2023-02-13 22:40:05 +02:00 committed by Rafael J. Wysocki
parent faffb0831a
commit 3082d7efd7
1 changed files with 24 additions and 11 deletions
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35
Documentation/firmware-guide/acpi/gpio-properties.rst
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@ -67,17 +67,30 @@ state of the output pin which driver should use during its initialization.
Linux tries to use common sense here and derives the state from the bias
and polarity settings. The table below shows the expectations:
========= ============= ==============
Pull Bias Polarity Requested...
========= ============= ==============
Implicit x AS IS (assumed firmware configured for us)
Explicit x (no _DSD) as Pull Bias (Up == High, Down == Low),
assuming non-active (Polarity = !Pull Bias)
Down Low as low, assuming active
Down High as low, assuming non-active
Up Low as high, assuming non-active
Up High as high, assuming active
========= ============= ==============
+-------------+-------------+-----------------------------------------------+
| Pull Bias | Polarity | Requested... |
+=============+=============+===============================================+
| Implicit |
+-------------+-------------+-----------------------------------------------+
| **Default** | x | AS IS (assumed firmware configured it for us) |
+-------------+-------------+-----------------------------------------------+
| Explicit |
+-------------+-------------+-----------------------------------------------+
| **None** | x | AS IS (assumed firmware configured it for us) |
| | | with no Pull Bias |
+-------------+-------------+-----------------------------------------------+
| **Up** | x (no _DSD) | |
| +-------------+ as high, assuming non-active |
| | Low | |
| +-------------+-----------------------------------------------+
| | High | as high, assuming active |
+-------------+-------------+-----------------------------------------------+
| **Down** | x (no _DSD) | |
| +-------------+ as low, assuming non-active |
| | High | |
| +-------------+-----------------------------------------------+
| | Low | as low, assuming active |
+-------------+-------------+-----------------------------------------------+
That said, for our above example the both GPIOs, since the bias setting
is explicit and _DSD is present, will be treated as active with a high