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 ====================
 S3C24XX GPIO Control
 ====================
 
 Introduction
 ------------
 
   The s3c2410 kernel provides an interface to configure and
   manipulate the state of the GPIO pins, and find out other
   information about them.
 
   There are a number of conditions attached to the configuration
   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.rst for the core implementation.
 
 
 GPIOLIB
 -------
 
   With the event of the GPIOLIB in drivers/gpio, support for some
   of the GPIO functions such as reading and writing a pin will
   be removed in favour of this common access method.
 
   Once all the extant drivers have been converted, the functions
   listed below will be removed (they may be marked as __deprecated
   in the near future).
 
   The following functions now either have a `s3c_` specific variant
   or are merged into gpiolib. See the definitions in
   arch/arm/mach-s3c/gpio-cfg.h:
 
   - s3c2410_gpio_setpin()       gpio_set_value() or gpio_direction_output()
   - s3c2410_gpio_getpin()       gpio_get_value() or gpio_direction_input()
   - s3c2410_gpio_getirq()       gpio_to_irq()
   - s3c2410_gpio_cfgpin()       s3c_gpio_cfgpin()
   - s3c2410_gpio_getcfg()       s3c_gpio_getcfg()
   - s3c2410_gpio_pullup()       s3c_gpio_setpull()
 
 
 GPIOLIB conversion
 ------------------
 
 If you need to convert your board or driver to use gpiolib from the phased
 out 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() changes have the problem that while 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 replaceable 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
 -------
 
   See arch/arm/mach-s3c/regs-gpio-s3c24xx.h for the list
   of GPIO pins, and the configuration values for them. This
   is included by using #include <mach/regs-gpio.h>
 
 
 PIN Numbers
 -----------
 
   Each pin has an unique number associated with it in regs-gpio.h,
   e.g. S3C2410_GPA(0) or S3C2410_GPF(1). These defines are used to tell
   the GPIO functions which pin is to be used.
 
   With the conversion to gpiolib, there is no longer a direct conversion
   from gpio pin number to register base address as in earlier kernels. This
   is due to the number space required for newer SoCs where the later
   GPIOs are not contiguous.
 
 
 Configuring a pin
 -----------------
 
   The following function allows the configuration of a given pin to
   be changed.
 
     void s3c_gpio_cfgpin(unsigned int pin, unsigned int function);
 
   e.g.:
 
      s3c_gpio_cfgpin(S3C2410_GPA(0), S3C_GPIO_SFN(1));
      s3c_gpio_cfgpin(S3C2410_GPE(8), S3C_GPIO_SFN(2));
 
    which would turn GPA(0) into the lowest Address line A0, and set
    GPE(8) to be connected to the SDIO/MMC controller's SDDAT1 line.
 
 
 Reading the current configuration
 ---------------------------------
 
   The current configuration of a pin can be read by using standard
   gpiolib function:
 
   s3c_gpio_getcfg(unsigned int pin);
 
   The return value will be from the same set of values which can be
   passed to s3c_gpio_cfgpin().
 
 
 Configuring a pull-up resistor
 ------------------------------
 
   A large proportion of the GPIO pins on the S3C2410 can have weak
   pull-up resistors enabled. This can be configured by the following
   function:
 
     void s3c_gpio_setpull(unsigned int pin, unsigned int to);
 
   Where the to value is S3C_GPIO_PULL_NONE to set the pull-up off,
   and S3C_GPIO_PULL_UP to enable the specified pull-up. Any other
   values are currently undefined.
 
 
 Getting and setting the state of a PIN
 --------------------------------------
 
   These calls are now implemented by the relevant gpiolib calls, convert
   your board or driver to use gpiolib.
 
 
 Getting the IRQ number associated with a PIN
 --------------------------------------------
 
   A standard gpiolib function can map the given pin number to an IRQ
   number to pass to the IRQ system.
 
    int gpio_to_irq(unsigned int pin);
 
   Note, not all pins have an IRQ.
 
 
 Author
 -------
 
 Ben Dooks, 03 October 2004
 Copyright 2004 Ben Dooks, Simtec Electronics

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