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authorAndy Shevchenko <andriy.shevchenko@linux.intel.com>2021-04-24 17:39:35 +0300
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2021-04-28 19:11:13 +0200
commitec3576eac11d66a388b6cba6a7cfb3b45039a712 (patch)
tree721b03b962d00a18157f1d53f974bc732a490505 /Documentation/firmware-guide
parentd8f9176b4ece17e831306072678cd9ae49688cf5 (diff)
Documentation: firmware-guide: gpio-properties: Add note to SPI CS case
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> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'Documentation/firmware-guide')
-rw-r--r--Documentation/firmware-guide/acpi/gpio-properties.rst6
1 files changed, 6 insertions, 0 deletions
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
==========================