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gpio interface loosens call restrictions

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Loosen gpio_{request,free}() and gpio_direction_{in,out}put() call context
restrictions slightly, so a common idiom is no longer an error: board init
code setting up spinlock-safe GPIOs before tasking is enabled.

The issue was caught by some paranoid code with might_sleep() checks.  The
legacy platform-specific GPIO interfaces stick to spinlock-safe GPIOs, so this
change reflects current implementations and won't break anything.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
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 2007-05-16 22:11:13 -07:00 committed by Linus Torvalds
parent 621e59a771
commit 83c6590cb8
1 changed files with 6 additions and 2 deletions
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8
Documentation/gpio.txt
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@ -111,7 +111,9 @@ setting up a platform_device using the GPIO, is mark its direction:
The return value is zero for success, else a negative errno. It should
be checked, since the get/set calls don't have error returns and since
misconfiguration is possible. (These calls could sleep.)
misconfiguration is possible. You should normally issue these calls from
a task context. However, for spinlock-safe GPIOs it's OK to use them
before tasking is enabled, as part of early board setup.
For output GPIOs, the value provided becomes the initial output value.
This helps avoid signal glitching during system startup.
@ -197,7 +199,9 @@ However, many platforms don't currently support this mechanism.
Passing invalid GPIO numbers to gpio_request() will fail, as will requesting
GPIOs that have already been claimed with that call. The return value of
gpio_request() must be checked. (These calls could sleep.)
gpio_request() must be checked. You should normally issue these calls from
a task context. However, for spinlock-safe GPIOs it's OK to request GPIOs
before tasking is enabled, as part of early board setup.
These calls serve two basic purposes. One is marking the signals which
are actually in use as GPIOs, for better diagnostics; systems may have