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gpiolib: request/free hooks

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Add a new internal mechanism to gpiolib to support low power
operations by letting gpio_chip instances see when their GPIOs
are in use.  When no GPIOs are active, chips may be able to
enter lower powered runtime states by disabling clocks and/or
power domains.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: "Magnus Damm" <magnus.damm@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Brownell
2008-10-15 22:03:16 -07:00
committed by Linus Torvalds
parent 93a22f8b95
commit 35e8bb5175
3 changed files with 91 additions and 13 deletions
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4
Documentation/gpio.txt
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@@ -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,