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| author | Paul Mundt <lethal@linux-sh.org> | 2008-10-20 11:17:52 +0900 |
|---|---|---|
| committer | Paul Mundt <lethal@linux-sh.org> | 2008-10-20 11:17:52 +0900 |
| commit | 4cb40f795af36b3deb743f6ccf6c3fd542c61c8d (patch) | |
| tree | db3d7519932549bf528f5b8e4cb8350356cd544d /Documentation/gpio.txt | |
| parent | 79ed2a9216dd3cc35c4f2c5dbaddadb195af83ac (diff) | |
| parent | 0cfd81031a26717fe14380d18275f8e217571615 (diff) | |
| download | kernel-crypto-4cb40f795af36b3deb743f6ccf6c3fd542c61c8d.tar.gz kernel-crypto-4cb40f795af36b3deb743f6ccf6c3fd542c61c8d.tar.xz kernel-crypto-4cb40f795af36b3deb743f6ccf6c3fd542c61c8d.zip | |
Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
Conflicts:
Documentation/kernel-parameters.txt
arch/sh/include/asm/elf.h
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 |