diff options
| author | Dirk Behme | 2015-07-18 08:02:07 +0200 |
|---|---|---|
| committer | Linus Walleij | 2015-08-17 10:38:52 +0200 |
| commit | ac49fbd1f9d437cca7234473850aef4165779383 (patch) | |
| tree | 07dee9262bbbee6ecf1adfba2b632dfe21873a65 /Documentation/gpio | |
| parent | 929550b9f9f870d73489df98318a740183c2e955 (diff) | |
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.txt | 33 |
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: |