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>

drivers/gpio/gpiolib.c

@@ -792,6 +792,8 @@ void gpio_free(unsigned gpio)
 	unsigned long		flags;
 	struct gpio_desc	*desc;
 
+	might_sleep();
+
 	if (!gpio_is_valid(gpio)) {
 		WARN_ON(extra_checks);
 		return;

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 int gpio_request(unsigned gpio, const char *label)
 
 static inline void gpio_free(unsigned gpio)
 {
+	might_sleep();
+
 	/* GPIO can never have been requested */
 	WARN_ON(1);
 }