On 18.07.2015 08:02, Dirk Behme wrote:
I've been searching for any documentation of 'the active-low property of a GPIO'
already mentioned in this documenation. But couldn't find any. Add it.
Sigend-off-by: Dirk Behme <[email protected]>
Acked-by: Alexandre Courbot <[email protected]>
---
Changes in v2: Incorporate the review comments from Alexandre.
Documentation/gpio/consumer.txt | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 75542b9..df7c51a 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -237,6 +237,39 @@ Note that these functions should only be used with great
moderation ; a driver
should not have to care about the physical line level.
+The active-low property
+-----------------------
+
+As a driver should not have to care about the physical line level, all of the
+gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
+the *logical* value. With this they take the active-low property into account.
+This does mean that they check whether the GPIO is configured to be active-low.
+And if so, they manipulate the passed value before the physical line level is
+driven.
+
+With this, all the gpiod_set_(array)_value_xxx() functions interpret the
parameter
+"value" as "active" ("1") or "inactive" ("0"). The physical line level will be
+driven accordingly.
+
+As an example, if the active-low poperty for a dedicated GPIO is set, and the
+gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level
will be
+driven low.
+
+To summarize:
+
+Function (example) active-low proporty physical line
+gpiod_set_raw_value(desc, 0); don't care low
+gpiod_set_raw_value(desc, 1); don't care high
+gpiod_set_value(desc, 0); default (active-high) low
+gpiod_set_value(desc, 1); default (active-high) high
+gpiod_set_value(desc, 0); active-low high
+gpiod_set_value(desc, 1); active-low low
+
+Please note again that the set_raw/get_raw functions should be avoided as much
+as possible, especially by drivers which should not care about the actual
physical
+line level and worry about the logical value instead.
+
+
Set multiple GPIO outputs with a single function call
-----------------------------------------------------
The following functions set the output values of an array of GPIOs:
Any further comments on this? Could this be applied?
Dirk
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