diff options
| author | Arjan van de Ven <arjan@linux.intel.com> | 2008-10-17 09:20:26 -0700 |
|---|---|---|
| committer | Arjan van de Ven <arjan@linux.intel.com> | 2008-10-17 09:20:26 -0700 |
| commit | 651dab4264e4ba0e563f5ff56f748127246e9065 (patch) | |
| tree | 016630974bdcb00fe529b673f96d389e0fd6dc94 /Documentation/gpio.txt | |
| parent | 40b8606253552109815786e5d4b0de98782d31f5 (diff) | |
| parent | 2e532d68a2b3e2aa6b19731501222069735c741c (diff) | |
Merge commit 'linus/master' into merge-linus
Conflicts:
arch/x86/kvm/i8254.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 18022e249c5..b1b98870124 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 |