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authorDavid Brownell <david-b@pacbell.net>2007-05-17 01:11:13 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-05-17 08:23:05 -0400
commit83c6590cb83d3106df12fee36ac2a261951b8c88 (patch)
tree8906e0f3366959e2595d26d263ab32922958743b /Documentation/gpio.txt
parent621e59a771f310358ade8f14cb745d5d5f1c410e (diff)
gpio interface loosens call restrictions
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>
Diffstat (limited to 'Documentation/gpio.txt')
-rw-r--r--Documentation/gpio.txt8
1 files changed, 6 insertions, 2 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index e8be0abb346c..36af58eba136 100644
--- a/Documentation/gpio.txt
+++ b/Documentation/gpio.txt
@@ -111,7 +111,9 @@ setting up a platform_device using the GPIO, is mark its direction:
111 111
112The return value is zero for success, else a negative errno. It should 112The return value is zero for success, else a negative errno. It should
113be checked, since the get/set calls don't have error returns and since 113be checked, since the get/set calls don't have error returns and since
114misconfiguration is possible. (These calls could sleep.) 114misconfiguration is possible. You should normally issue these calls from
115a task context. However, for spinlock-safe GPIOs it's OK to use them
116before tasking is enabled, as part of early board setup.
115 117
116For output GPIOs, the value provided becomes the initial output value. 118For output GPIOs, the value provided becomes the initial output value.
117This helps avoid signal glitching during system startup. 119This helps avoid signal glitching during system startup.
@@ -197,7 +199,9 @@ However, many platforms don't currently support this mechanism.
197 199
198Passing invalid GPIO numbers to gpio_request() will fail, as will requesting 200Passing invalid GPIO numbers to gpio_request() will fail, as will requesting
199GPIOs that have already been claimed with that call. The return value of 201GPIOs that have already been claimed with that call. The return value of
200gpio_request() must be checked. (These calls could sleep.) 202gpio_request() must be checked. You should normally issue these calls from
203a task context. However, for spinlock-safe GPIOs it's OK to request GPIOs
204before tasking is enabled, as part of early board setup.
201 205
202These calls serve two basic purposes. One is marking the signals which 206These calls serve two basic purposes. One is marking the signals which
203are actually in use as GPIOs, for better diagnostics; systems may have 207are actually in use as GPIOs, for better diagnostics; systems may have