diff options
Diffstat (limited to 'kernel/Documentation/gpio/consumer.txt')
| -rw-r--r-- | kernel/Documentation/gpio/consumer.txt | 66 |
1 files changed, 51 insertions, 15 deletions
diff --git a/kernel/Documentation/gpio/consumer.txt b/kernel/Documentation/gpio/consumer.txt index c21c1313f..e000502fd 100644 --- a/kernel/Documentation/gpio/consumer.txt +++ b/kernel/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: @@ -237,22 +240,55 @@ 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: - void gpiod_set_array(unsigned int array_size, - struct gpio_desc **desc_array, - int *value_array) - void gpiod_set_raw_array(unsigned int array_size, - struct gpio_desc **desc_array, - int *value_array) - void gpiod_set_array_cansleep(unsigned int array_size, - struct gpio_desc **desc_array, - int *value_array) - void gpiod_set_raw_array_cansleep(unsigned int array_size, - struct gpio_desc **desc_array, - int *value_array) + void gpiod_set_array_value(unsigned int array_size, + struct gpio_desc **desc_array, + int *value_array) + void gpiod_set_raw_array_value(unsigned int array_size, + struct gpio_desc **desc_array, + int *value_array) + void gpiod_set_array_value_cansleep(unsigned int array_size, + struct gpio_desc **desc_array, + int *value_array) + void gpiod_set_raw_array_value_cansleep(unsigned int array_size, + struct gpio_desc **desc_array, + int *value_array) The array can be an arbitrary set of GPIOs. The functions will try to set GPIOs belonging to the same bank or chip simultaneously if supported by the @@ -271,8 +307,8 @@ matches the desired group of GPIOs, those GPIOs can be set by simply using the struct gpio_descs returned by gpiod_get_array(): struct gpio_descs *my_gpio_descs = gpiod_get_array(...); - gpiod_set_array(my_gpio_descs->ndescs, my_gpio_descs->desc, - my_gpio_values); + gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc, + my_gpio_values); It is also possible to set a completely arbitrary array of descriptors. The descriptors may be obtained using any combination of gpiod_get() and @@ -290,7 +326,7 @@ corresponding to a given GPIO using the following call: int gpiod_to_irq(const struct gpio_desc *desc) -It will return an IRQ number, or an negative errno code if the mapping can't be +It will return an IRQ number, or a negative errno code if the mapping can't be done (most likely because that particular GPIO cannot be used as IRQ). It is an unchecked error to use a GPIO that wasn't set up as an input using gpiod_direction_input(), or to use an IRQ number that didn't originally come |