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Diffstat (limited to 'Documentation/arm/Samsung-S3C24XX/GPIO.txt')
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diff --git a/Documentation/arm/Samsung-S3C24XX/GPIO.txt b/Documentation/arm/Samsung-S3C24XX/GPIO.txt new file mode 100644 index 00000000..816d6071 --- /dev/null +++ b/Documentation/arm/Samsung-S3C24XX/GPIO.txt @@ -0,0 +1,214 @@ + S3C2410 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.txt for the core implemetation. + + +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/plat-samsung/include/plat/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 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 +------- + + See arch/arm/mach-s3c2410/include/mach/regs-gpio.h for the list + of GPIO pins, and the configuration values for them. This + is included by using #include <mach/regs-gpio.h> + + The GPIO management functions are defined in the hardware + header arch/arm/mach-s3c2410/include/mach/hardware.h which can be + included by #include <mach/hardware.h> + + A useful amount of documentation can be found in the hardware + header on how the GPIO functions (and others) work. + + Whilst a number of these functions do make some checks on what + is passed to them, for speed of use, they may not always ensure + that the user supplied data to them is correct. + + +PIN Numbers +----------- + + Each pin has an unique number associated with it in regs-gpio.h, + eg 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 s3c2410_gpio_cfgpin(unsigned int pin, unsigned int function); + + Eg: + + s3c2410_gpio_cfgpin(S3C2410_GPA(0), S3C2410_GPA0_ADDR0); + s3c2410_gpio_cfgpin(S3C2410_GPE(8), S3C2410_GPE8_SDDAT1); + + 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. + + The s3c_gpio_cfgpin() call is a functional replacement for this call. + + +Reading the current configuration +--------------------------------- + + The current configuration of a pin can be read by using: + + s3c2410_gpio_getcfg(unsigned int pin); + + The return value will be from the same set of values which can be + passed to s3c2410_gpio_cfgpin(). + + The s3c_gpio_getcfg() call should be a functional replacement for + this call. + + +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 s3c2410_gpio_pullup(unsigned int pin, unsigned int to); + + Where the to value is zero to set the pull-up off, and 1 to enable + the specified pull-up. Any other values are currently undefined. + + The s3c_gpio_setpull() offers similar functionality, but with the + ability to encode whether the pull is up or down. Currently there + is no 'just on' state, so up or down must be selected. + + +Getting the state of a PIN +-------------------------- + + The state of a pin can be read by using the function: + + unsigned int s3c2410_gpio_getpin(unsigned int pin); + + This will return either zero or non-zero. Do not count on this + function returning 1 if the pin is set. + + This call is now implemented by the relevant gpiolib calls, convert + your board or driver to use gpiolib. + + +Setting the state of a PIN +-------------------------- + + The value an pin is outputing can be modified by using the following: + + void s3c2410_gpio_setpin(unsigned int pin, unsigned int to); + + Which sets the given pin to the value. Use 0 to write 0, and 1 to + set the output to 1. + + This call is now implemented by the relevant gpiolib calls, convert + your board or driver to use gpiolib. + + +Getting the IRQ number associated with a PIN +-------------------------------------------- + + The following function can map the given pin number to an IRQ + number to pass to the IRQ system. + + int s3c2410_gpio_getirq(unsigned int pin); + + Note, not all pins have an IRQ. + + This call is now implemented by the relevant gpiolib calls, convert + your board or driver to use gpiolib. + + +Authour +------- + + +Ben Dooks, 03 October 2004 +Copyright 2004 Ben Dooks, Simtec Electronics |