aboutsummaryrefslogtreecommitdiff
path: root/Documentation/arm/Samsung-S3C24XX/GPIO.txt
diff options
context:
space:
mode:
authorFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
committerFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
commit3b4bd47f8f4ed3aaf7c81c9b5d2d37ad79fadf4a (patch)
treeb9996006addfd7ae70a39672b76843b49aebc189 /Documentation/arm/Samsung-S3C24XX/GPIO.txt
downloadlinux-linaro-highbank-3b4bd47f8f4ed3aaf7c81c9b5d2d37ad79fadf4a.tar.gz
Imported Upstream version 3.9.0HEADupstream/3.9.0upstreammaster
Diffstat (limited to 'Documentation/arm/Samsung-S3C24XX/GPIO.txt')
-rw-r--r--Documentation/arm/Samsung-S3C24XX/GPIO.txt182
1 files changed, 182 insertions, 0 deletions
diff --git a/Documentation/arm/Samsung-S3C24XX/GPIO.txt b/Documentation/arm/Samsung-S3C24XX/GPIO.txt
new file mode 100644
index 00000000..8b46c796
--- /dev/null
+++ b/Documentation/arm/Samsung-S3C24XX/GPIO.txt
@@ -0,0 +1,182 @@
+ 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.txt 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/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 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 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 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-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,
+ 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