ARM: S3C24XX: Documentation: add section on gpiolib changes

  s3c2410_gpio_pullup()		s3c_gpio_setpull()

GPIOLIB conversion

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If you need to convert your board or driver to use gpiolib from the exiting

s3c2410 api, then here are some notes on the process.

1) If your board is exclusively using an GPIO, say to control peripheral

   power, then it will require to claim the gpio with gpio_request() before

   it can use it.

   It is recommended to check the return value, with at least WARN_ON()

   during initialisation.

2) The s3c2410_gpio_cfgpin() can be directly replaced with s3c_gpio_cfgpin()

   as they have the same arguments, and can either take the pin specific

   values, or the more generic special-function-number arguments.

3) s3c2410_gpio_pullup() changs have the problem that whilst the 

   s3c2410_gpio_pullup(x, 1) can be easily translated to the

   s3c_gpio_setpull(x, S3C_GPIO_PULL_NONE), the s3c2410_gpio_pullup(x, 0)

   are not so easy.

   The s3c2410_gpio_pullup(x, 0) case enables the pull-up (or in the case

   of some of the devices, a pull-down) and as such the new API distinguishes

   between the UP and DOWN case. There is currently no 'just turn on' setting

   which may be required if this becomes a problem.

4) s3c2410_gpio_setpin() can be replaced by gpio_set_value(), the old call

   does not implicitly configure the relevant gpio to output. The gpio

   direction should be changed before using gpio_set_value().

5) s3c2410_gpio_getpin() is replaceable by gpio_get_value() if the pin

   has been set to input. It is currently unknown what the behaviour is

   when using gpio_get_value() on an output pin (s3c2410_gpio_getpin

   would return the value the pin is supposed to be outputting).

6) s3c2410_gpio_getirq() should be directly replacable with the

   gpio_to_irq() call.

The s3c2410_gpio and gpio_ calls have always operated on the same gpio

numberspace, so there is no problem with converting the gpio numbering

between the calls.

Headers

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