gpio.rst 5.5 KB

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  1. ====================
  2. S3C24XX GPIO Control
  3. ====================
  4. Introduction
  5. ------------
  6. The s3c2410 kernel provides an interface to configure and
  7. manipulate the state of the GPIO pins, and find out other
  8. information about them.
  9. There are a number of conditions attached to the configuration
  10. of the s3c2410 GPIO system, please read the Samsung provided
  11. data-sheet/users manual to find out the complete list.
  12. See Documentation/arm/samsung/gpio.rst for the core implementation.
  13. GPIOLIB
  14. -------
  15. With the event of the GPIOLIB in drivers/gpio, support for some
  16. of the GPIO functions such as reading and writing a pin will
  17. be removed in favour of this common access method.
  18. Once all the extant drivers have been converted, the functions
  19. listed below will be removed (they may be marked as __deprecated
  20. in the near future).
  21. The following functions now either have a `s3c_` specific variant
  22. or are merged into gpiolib. See the definitions in
  23. arch/arm/plat-samsung/include/plat/gpio-cfg.h:
  24. - s3c2410_gpio_setpin() gpio_set_value() or gpio_direction_output()
  25. - s3c2410_gpio_getpin() gpio_get_value() or gpio_direction_input()
  26. - s3c2410_gpio_getirq() gpio_to_irq()
  27. - s3c2410_gpio_cfgpin() s3c_gpio_cfgpin()
  28. - s3c2410_gpio_getcfg() s3c_gpio_getcfg()
  29. - s3c2410_gpio_pullup() s3c_gpio_setpull()
  30. GPIOLIB conversion
  31. ------------------
  32. If you need to convert your board or driver to use gpiolib from the phased
  33. out s3c2410 API, then here are some notes on the process.
  34. 1) If your board is exclusively using an GPIO, say to control peripheral
  35. power, then it will require to claim the gpio with gpio_request() before
  36. it can use it.
  37. It is recommended to check the return value, with at least WARN_ON()
  38. during initialisation.
  39. 2) The s3c2410_gpio_cfgpin() can be directly replaced with s3c_gpio_cfgpin()
  40. as they have the same arguments, and can either take the pin specific
  41. values, or the more generic special-function-number arguments.
  42. 3) s3c2410_gpio_pullup() changes have the problem that while the
  43. s3c2410_gpio_pullup(x, 1) can be easily translated to the
  44. s3c_gpio_setpull(x, S3C_GPIO_PULL_NONE), the s3c2410_gpio_pullup(x, 0)
  45. are not so easy.
  46. The s3c2410_gpio_pullup(x, 0) case enables the pull-up (or in the case
  47. of some of the devices, a pull-down) and as such the new API distinguishes
  48. between the UP and DOWN case. There is currently no 'just turn on' setting
  49. which may be required if this becomes a problem.
  50. 4) s3c2410_gpio_setpin() can be replaced by gpio_set_value(), the old call
  51. does not implicitly configure the relevant gpio to output. The gpio
  52. direction should be changed before using gpio_set_value().
  53. 5) s3c2410_gpio_getpin() is replaceable by gpio_get_value() if the pin
  54. has been set to input. It is currently unknown what the behaviour is
  55. when using gpio_get_value() on an output pin (s3c2410_gpio_getpin
  56. would return the value the pin is supposed to be outputting).
  57. 6) s3c2410_gpio_getirq() should be directly replaceable with the
  58. gpio_to_irq() call.
  59. The s3c2410_gpio and `gpio_` calls have always operated on the same gpio
  60. numberspace, so there is no problem with converting the gpio numbering
  61. between the calls.
  62. Headers
  63. -------
  64. See arch/arm/mach-s3c24xx/include/mach/regs-gpio.h for the list
  65. of GPIO pins, and the configuration values for them. This
  66. is included by using #include <mach/regs-gpio.h>
  67. PIN Numbers
  68. -----------
  69. Each pin has an unique number associated with it in regs-gpio.h,
  70. e.g. S3C2410_GPA(0) or S3C2410_GPF(1). These defines are used to tell
  71. the GPIO functions which pin is to be used.
  72. With the conversion to gpiolib, there is no longer a direct conversion
  73. from gpio pin number to register base address as in earlier kernels. This
  74. is due to the number space required for newer SoCs where the later
  75. GPIOs are not contiguous.
  76. Configuring a pin
  77. -----------------
  78. The following function allows the configuration of a given pin to
  79. be changed.
  80. void s3c_gpio_cfgpin(unsigned int pin, unsigned int function);
  81. e.g.:
  82. s3c_gpio_cfgpin(S3C2410_GPA(0), S3C_GPIO_SFN(1));
  83. s3c_gpio_cfgpin(S3C2410_GPE(8), S3C_GPIO_SFN(2));
  84. which would turn GPA(0) into the lowest Address line A0, and set
  85. GPE(8) to be connected to the SDIO/MMC controller's SDDAT1 line.
  86. Reading the current configuration
  87. ---------------------------------
  88. The current configuration of a pin can be read by using standard
  89. gpiolib function:
  90. s3c_gpio_getcfg(unsigned int pin);
  91. The return value will be from the same set of values which can be
  92. passed to s3c_gpio_cfgpin().
  93. Configuring a pull-up resistor
  94. ------------------------------
  95. A large proportion of the GPIO pins on the S3C2410 can have weak
  96. pull-up resistors enabled. This can be configured by the following
  97. function:
  98. void s3c_gpio_setpull(unsigned int pin, unsigned int to);
  99. Where the to value is S3C_GPIO_PULL_NONE to set the pull-up off,
  100. and S3C_GPIO_PULL_UP to enable the specified pull-up. Any other
  101. values are currently undefined.
  102. Getting and setting the state of a PIN
  103. --------------------------------------
  104. These calls are now implemented by the relevant gpiolib calls, convert
  105. your board or driver to use gpiolib.
  106. Getting the IRQ number associated with a PIN
  107. --------------------------------------------
  108. A standard gpiolib function can map the given pin number to an IRQ
  109. number to pass to the IRQ system.
  110. int gpio_to_irq(unsigned int pin);
  111. Note, not all pins have an IRQ.
  112. Author
  113. -------
  114. Ben Dooks, 03 October 2004
  115. Copyright 2004 Ben Dooks, Simtec Electronics