ARM: SAMSUNG: Documentation: add documentation on GPIO code

Add some documentation in Documentation/arm/Samsung for the GPIO code
and where to look for the necessary functions. Update the S3C24XX case
as well.
Signed-off-by: NBen Dooks <ben-linux@fluff.org>

Documentation/arm/Samsung-S3C24XX/GPIO.txt

@@ -12,6 +12,8 @@ Introduction
   of the s3c2410 GPIO system, please read the Samsung provided
   data-sheet/users manual to find out the complete list.
 
+  See Documentation/arm/Samsung/GPIO.txt for the core implemetation.
+
 
 GPIOLIB
 -------

Documentation/arm/Samsung-S3C24XX/Overview.txt

@@ -218,6 +218,10 @@ GPIO
   As of v2.6.34, the move towards using gpiolib support is almost
   complete, and very little of the old calls are left.
 
+  See Documentation/arm/Samsung-S3C24XX/GPIO.txt for the S3C24XX specific
+  support and Documentation/arm/Samsung/GPIO.txt for the core Samsung
+  implementation.
+
 
 Clock Management
 ----------------

Documentation/arm/Samsung/GPIO.txt

+		Samsung GPIO implementation
+		===========================
+
+Introduction
+------------
+
+This outlines the Samsung GPIO implementation and the architecture
+specfic calls provided alongisde the drivers/gpio core.
+
+
+S3C24XX (Legacy)
+----------------
+
+See Documentation/arm/Samsung-S3C24XX/GPIO.txt for more information
+about these devices. Their implementation is being brought into line
+with the core samsung implementation described in this document.
+
+
+GPIOLIB integration
+-------------------
+
+The gpio implementation uses gpiolib as much as possible, only providing
+specific calls for the items that require Samsung specific handling, such
+as pin special-function or pull resistor control.
+
+GPIO numbering is synchronised between the Samsung and gpiolib system.
+
+
+PIN configuration
+-----------------
+
+Pin configuration is specific to the Samsung architecutre, with each SoC
+registering the necessary information for the core gpio configuration
+implementation to configure pins as necessary.
+
+The s3c_gpio_cfgpin() and s3c_gpio_setpull() provide the means for a
+driver or machine to change gpio configuration.
+
+See arch/arm/plat-samsung/include/plat/gpio-cfg.h for more information
+on these functions.
+
+