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authorAndré Fabian Silva Delgado <emulatorman@parabola.nu>2015-12-15 14:52:16 -0300
committerAndré Fabian Silva Delgado <emulatorman@parabola.nu>2015-12-15 14:52:16 -0300
commit8d91c1e411f55d7ea91b1183a2e9f8088fb4d5be (patch)
treee9891aa6c295060d065adffd610c4f49ecf884f3 /Documentation/gpio/consumer.txt
parenta71852147516bc1cb5b0b3cbd13639bfd4022dc8 (diff)
Linux-libre 4.3.2-gnu
Diffstat (limited to 'Documentation/gpio/consumer.txt')
-rw-r--r--Documentation/gpio/consumer.txt36
1 files changed, 36 insertions, 0 deletions
diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 75542b91b..e000502fd 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -39,6 +39,9 @@ device that displays digits), an additional index argument can be specified:
const char *con_id, unsigned int idx,
enum gpiod_flags flags)
+For a more detailed description of the con_id parameter in the DeviceTree case
+see Documentation/gpio/board.txt
+
The flags parameter is used to optionally specify a direction and initial value
for the GPIO. Values can be:
@@ -237,6 +240,39 @@ 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 means 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 property 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: