[PATCH] gpio_direction_output() needs an initial value

It's been pointed out that output GPIOs should have an initial value, to
avoid signal glitching ...  among other things, it can be some time before
a driver is ready.  This patch corrects that oversight, fixing

 - documentation
 - platforms supporting the GPIO interface
 - users of that call (just one for now, others are pending)

There's only one user of this call for now since most platforms are still
using non-generic GPIO setup code, which in most cases already couples the
initial value with its "set output mode" request.

Note that most platforms are clear about the hardware letting the output
value be set before the pin direction is changed, but the s3c241x docs are
vague on that topic ...  so those chips might not avoid the glitches.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Andrew Victor <andrew@sanpeople.com>
Acked-by: Milan Svoboda <msvoboda@ra.rockwell.com>
Acked-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/asm-arm/arch-s3c2410/gpio.h b/include/asm-arm/arch-s3c2410/gpio.h
index d47ae453f8ca..7583895fd336 100644
--- a/include/asm-arm/arch-s3c2410/gpio.h
+++ b/include/asm-arm/arch-s3c2410/gpio.h
@@ -44,9 +44,11 @@ static inline int gpio_direction_input(unsigned gpio)
         return 0;
 }
 
-static inline int gpio_direction_output(unsigned gpio)
+static inline int gpio_direction_output(unsigned gpio, int value)
 {
         s3c2410_gpio_cfgpin(gpio, S3C2410_GPIO_OUTPUT);
+        /* REVISIT can we write the value first, to avoid glitching? */
+        s3c2410_gpio_setpin(gpio, value);
         return 0;
 }