diff options
| author | Ingo Molnar <mingo@elte.hu> | 2008-12-31 08:31:57 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-12-31 08:31:57 +0100 |
| commit | a9de18eb761f7c1c860964b2e5addc1a35c7e861 (patch) | |
| tree | 886e75fdfd09690cd262ca69cb7f5d1d42b48602 /Documentation/gpio.txt | |
| parent | b2aaf8f74cdc84a9182f6cabf198b7763bcb9d40 (diff) | |
| parent | 6a94cb73064c952255336cc57731904174b2c58f (diff) | |
Merge branch 'linus' into stackprotector
Conflicts:
arch/x86/include/asm/pda.h
kernel/fork.c
Diffstat (limited to 'Documentation/gpio.txt')
| -rw-r--r-- | Documentation/gpio.txt | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index 18022e249c53..b1b988701247 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -240,6 +240,10 @@ signal, or (b) something wrongly believes it's safe to remove drivers needed to manage a signal that's in active use. That is, requesting a GPIO can serve as a kind of lock. +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. + These two calls are optional because not not all current Linux platforms offer such functionality in their GPIO support; a valid implementation could return success for all gpio_request() calls. Unlike the other calls, @@ -264,7 +268,7 @@ map between them using calls like: /* map GPIO numbers to IRQ numbers */ int gpio_to_irq(unsigned gpio); - /* map IRQ numbers to GPIO numbers */ + /* map IRQ numbers to GPIO numbers (avoid using this) */ int irq_to_gpio(unsigned irq); Those return either the corresponding number in the other namespace, or @@ -284,7 +288,8 @@ system wakeup capabilities. Non-error values returned from irq_to_gpio() would most commonly be used with gpio_get_value(), for example to initialize or update driver state -when the IRQ is edge-triggered. +when the IRQ is edge-triggered. Note that some platforms don't support +this reverse mapping, so you should avoid using it. Emulating Open Drain Signals |