diff options
Diffstat (limited to 'Documentation/gpio.txt')
| -rw-r--r-- | Documentation/gpio.txt | 35 |
1 files changed, 29 insertions, 6 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index c2c6e9b39bb..d96a6dba574 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -158,10 +158,11 @@ and configure pullups/pulldowns appropriately.) Spinlock-Safe GPIO access ------------------------- Most GPIO controllers can be accessed with memory read/write instructions. -That doesn't need to sleep, and can safely be done from inside IRQ handlers. -(That includes hardirq contexts on RT kernels.) +Those don't need to sleep, and can safely be done from inside hard +(nonthreaded) IRQ handlers and similar contexts. -Use these calls to access such GPIOs: +Use the following calls to access such GPIOs, +for which gpio_cansleep() will always return false (see below): /* GPIO INPUT: return zero or nonzero */ int gpio_get_value(unsigned gpio); @@ -210,9 +211,31 @@ To access such GPIOs, a different set of accessors is defined: /* GPIO OUTPUT, might sleep */ void gpio_set_value_cansleep(unsigned gpio, int value); -Other than the fact that these calls might sleep, and will not be ignored -for GPIOs that can't be accessed from IRQ handlers, these calls act the -same as the spinlock-safe calls. + +Accessing such GPIOs requires a context which may sleep, for example +a threaded IRQ handler, and those accessors must be used instead of +spinlock-safe accessors without the cansleep() name suffix. + +Other than the fact that these accessors might sleep, and will work +on GPIOs that can't be accessed from hardIRQ handlers, these calls act +the same as the spinlock-safe calls. + + ** IN ADDITION ** calls to setup and configure such GPIOs must be made +from contexts which may sleep, since they may need to access the GPIO +controller chip too: (These setup calls are usually made from board +setup or driver probe/teardown code, so this is an easy constraint.) + + gpio_direction_input() + gpio_direction_output() + gpio_request() + +## gpio_request_one() +## gpio_request_array() +## gpio_free_array() + + gpio_free() + gpio_set_debounce() + Claiming and Releasing GPIOs |