path: root/Documentation
diff options
authorDavid Brownell <>2010-08-10 18:02:24 -0700
committerLinus Torvalds <>2010-08-11 08:59:08 -0700
commit9c4ba9466117b16a2b85034bb87db528aaeb3f07 (patch)
tree24ca585f76deef20b8c541ec2b62a1c72776a931 /Documentation
parent49946f68149a723659eca253376ac555d4b73280 (diff)
gpiolib: decouple might_sleep_if() from DEBUG
Be more consistent about runtime programming interface abuse warnings, which can reduce some confusion and trigger bugfixes. Based on an observation and patch from Jani Nikula. Also update doc to highlight some sleeping-call issues and to match some recent changes. Signed-off-by: David Brownell <> Cc: Jani Nikula <> Cc: "Ryan Mallon" <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'Documentation')
1 files changed, 29 insertions, 6 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index c2c6e9b39bbe..d96a6dba5748 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