gpio_free might sleep, generic part

According to the documentation gpio_free should only be called from task
context only.  To make this more explicit add a might sleep to all
implementations.

This is the generic part which changes gpiolib and the fallback
implementation only.

Signed-off-by: Uwe Kleine-König <ukleinek@informatik.uni-freiburg.de>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/gpio.h b/include/linux/gpio.h
index 730a20b..e10c49a 100644
--- a/include/linux/gpio.h
+++ b/include/linux/gpio.h
@@ -8,6 +8,7 @@
 
 #else
 
+#include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/errno.h>
 
@@ -32,6 +33,8 @@
 
 static inline void gpio_free(unsigned gpio)
 {
+	might_sleep();
+
 	/* GPIO can never have been requested */
 	WARN_ON(1);
 }