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authorDirk Behme <dirk.behme@gmail.com>2015-07-18 08:02:07 +0200
committerLinus Walleij <linus.walleij@linaro.org>2015-08-17 10:38:52 +0200
commitac49fbd1f9d437cca7234473850aef4165779383 (patch)
tree07dee9262bbbee6ecf1adfba2b632dfe21873a65 /Documentation/gpio
parent929550b9f9f870d73489df98318a740183c2e955 (diff)
downloadlinux-ac49fbd1f9d437cca7234473850aef4165779383.tar.bz2
Documentation: gpio: consumer: describe active low property
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 <dirk.behme@gmail.com> Acked-by: Alexandre Courbot <acourbot@nvidia.com> [Spelling, grammar fixes] Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Diffstat (limited to 'Documentation/gpio')
-rw-r--r--Documentation/gpio/consumer.txt33
1 files changed, 33 insertions, 0 deletions
diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 75542b91b766..a206639454ab 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 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: