diff options
| -rw-r--r-- | Documentation/gpio.txt | 23 |
1 files changed, 20 insertions, 3 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index f783e7fed76..620a07844e8 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -271,9 +271,26 @@ Some platforms may also use knowledge about what GPIOs are active for power management, such as by powering down unused chip sectors and, more easily, gating off unused clocks. -Note that requesting a GPIO does NOT cause it to be configured in any -way; it just marks that GPIO as in use. Separate code must handle any -pin setup (e.g. controlling which pin the GPIO uses, pullup/pulldown). +For GPIOs that use pins known to the pinctrl subsystem, that subsystem should +be informed of their use; a gpiolib driver's .request() operation may call +pinctrl_request_gpio(), and a gpiolib driver's .free() operation may call +pinctrl_free_gpio(). The pinctrl subsystem allows a pinctrl_request_gpio() +to succeed concurrently with a pin or pingroup being "owned" by a device for +pin multiplexing. + +Any programming of pin multiplexing hardware that is needed to route the +GPIO signal to the appropriate pin should occur within a GPIO driver's +.direction_input() or .direction_output() operations, and occur after any +setup of an output GPIO's value. This allows a glitch-free migration from a +pin's special function to GPIO. This is sometimes required when using a GPIO +to implement a workaround on signals typically driven by a non-GPIO HW block. + +Some platforms allow some or all GPIO signals to be routed to different pins. +Similarly, other aspects of the GPIO or pin may need to be configured, such as +pullup/pulldown. Platform software should arrange that any such details are +configured prior to gpio_request() being called for those GPIOs, e.g. using +the pinctrl subsystem's mapping table, so that GPIO users need not be aware +of these details. Also note that it's your responsibility to have stopped using a GPIO before you free it. |