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]> --- Documentation/gpio/consumer.txt | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt index 75542b9..f1a6e20 100644 --- a/Documentation/gpio/consumer.txt +++ b/Documentation/gpio/consumer.txt @@ -236,6 +236,32 @@ The active-low state of a GPIO can also be queried using the following call: 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_xxx_value_xxx() functions do 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_xxx_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_xxx_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); n/a low +gpiod_set_value(desc, 1); n/a high +gpiod_set_value(desc, 0); active-low high +gpiod_set_value(desc, 1); active-low low + Set multiple GPIO outputs with a single function call ----------------------------------------------------- -- 2.4.5 -- To unsubscribe from this list: send the line "unsubscribe linux-gpio" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
