docs: gpio: explain GPIOD_OUT_* values and toggling active low
I was confused about the gpiod_flags values and thought that
GPIOD_OUT_LOW and GPIOD_OUT_HIGH set the line to be active low / active
high. This is not true, but I got the misconception because the flags
GPIOD_OUT_*_OPEN_DRAIN do change line configuration and there's a
subchapter about *active low* and *open drain* semantics.
Add an explicit mention that the initial value is a logical value (and
not the line configuration or physical line level). Also add a mention
of the function gpiod_toggle_active_low which was previously missing
from this document.
Signed-off-by: Hannu Hartikainen <hannu@hrtk.in>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
diff --git a/Documentation/driver-api/gpio/consumer.rst b/Documentation/driver-api/gpio/consumer.rst
index 3366a99..47869ca 100644
--- a/Documentation/driver-api/gpio/consumer.rst
+++ b/Documentation/driver-api/gpio/consumer.rst
@@ -72,6 +72,10 @@
* GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line
to be electrically used with open drain.
+Note that the initial value is *logical* and the physical line level depends on
+whether the line is configured active high or active low (see
+:ref:`active_low_semantics`).
+
The two last flags are used for use cases where open drain is mandatory, such
as I2C: if the line is not already configured as open drain in the mappings
(see board.txt), then open drain will be enforced anyway and a warning will be
@@ -252,6 +256,8 @@
spinlock-safe calls.
+.. _active_low_semantics:
+
The active low and open drain semantics
---------------------------------------
As a consumer should not have to care about the physical line level, all of the
@@ -309,9 +315,11 @@
void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
-The active low state of a GPIO can also be queried using the following call::
+The active low state of a GPIO can also be queried and toggled using the
+following calls::
int gpiod_is_active_low(const struct gpio_desc *desc)
+ void gpiod_toggle_active_low(struct gpio_desc *desc)
Note that these functions should only be used with great moderation; a driver
should not have to care about the physical line level or open drain semantics.
