issues including wire-OR and output latencies.
The get/set calls have no error returns because "invalid GPIO" should have
-been reported earlier in gpio_set_direction(). However, note that not all
+been reported earlier from gpio_direction_*(). However, note that not all
platforms can read the value of output pins; those that can't should always
return zero. Also, using these calls for GPIOs that can't safely be accessed
without sleeping (see below) is an error.
Those return either the corresponding number in the other namespace, or
else a negative errno code if the mapping can't be done. (For example,
some GPIOs can't used as IRQs.) It is an unchecked error to use a GPIO
-number that hasn't been marked as an input using gpio_set_direction(), or
+number that wasn't set up as an input using gpio_direction_input(), or
to use an IRQ number that didn't originally come from gpio_to_irq().
These two mapping calls are expected to cost on the order of a single