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Documentation / arm / Samsung-S3C24XX / GPIO.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:00 EST.

1				S3C24XX GPIO Control
2				====================
3	
4	Introduction
5	------------
6	
7	  The s3c2410 kernel provides an interface to configure and
8	  manipulate the state of the GPIO pins, and find out other
9	  information about them.
10	
11	  There are a number of conditions attached to the configuration
12	  of the s3c2410 GPIO system, please read the Samsung provided
13	  data-sheet/users manual to find out the complete list.
14	
15	  See Documentation/arm/Samsung/GPIO.txt for the core implementation.
16	
17	
18	GPIOLIB
19	-------
20	
21	  With the event of the GPIOLIB in drivers/gpio, support for some
22	  of the GPIO functions such as reading and writing a pin will
23	  be removed in favour of this common access method.
24	
25	  Once all the extant drivers have been converted, the functions
26	  listed below will be removed (they may be marked as __deprecated
27	  in the near future).
28	
29	  The following functions now either have a s3c_ specific variant
30	  or are merged into gpiolib. See the definitions in
31	  arch/arm/plat-samsung/include/plat/gpio-cfg.h:
32	
33	  s3c2410_gpio_setpin()		gpio_set_value() or gpio_direction_output()
34	  s3c2410_gpio_getpin()		gpio_get_value() or gpio_direction_input()
35	  s3c2410_gpio_getirq()		gpio_to_irq()
36	  s3c2410_gpio_cfgpin()		s3c_gpio_cfgpin()
37	  s3c2410_gpio_getcfg()		s3c_gpio_getcfg()
38	  s3c2410_gpio_pullup()		s3c_gpio_setpull()
39	
40	
41	GPIOLIB conversion
42	------------------
43	
44	If you need to convert your board or driver to use gpiolib from the phased
45	out s3c2410 API, then here are some notes on the process.
46	
47	1) If your board is exclusively using an GPIO, say to control peripheral
48	   power, then it will require to claim the gpio with gpio_request() before
49	   it can use it.
50	
51	   It is recommended to check the return value, with at least WARN_ON()
52	   during initialisation.
53	
54	2) The s3c2410_gpio_cfgpin() can be directly replaced with s3c_gpio_cfgpin()
55	   as they have the same arguments, and can either take the pin specific
56	   values, or the more generic special-function-number arguments.
57	
58	3) s3c2410_gpio_pullup() changes have the problem that whilst the
59	   s3c2410_gpio_pullup(x, 1) can be easily translated to the
60	   s3c_gpio_setpull(x, S3C_GPIO_PULL_NONE), the s3c2410_gpio_pullup(x, 0)
61	   are not so easy.
62	
63	   The s3c2410_gpio_pullup(x, 0) case enables the pull-up (or in the case
64	   of some of the devices, a pull-down) and as such the new API distinguishes
65	   between the UP and DOWN case. There is currently no 'just turn on' setting
66	   which may be required if this becomes a problem.
67	
68	4) s3c2410_gpio_setpin() can be replaced by gpio_set_value(), the old call
69	   does not implicitly configure the relevant gpio to output. The gpio
70	   direction should be changed before using gpio_set_value().
71	
72	5) s3c2410_gpio_getpin() is replaceable by gpio_get_value() if the pin
73	   has been set to input. It is currently unknown what the behaviour is
74	   when using gpio_get_value() on an output pin (s3c2410_gpio_getpin
75	   would return the value the pin is supposed to be outputting).
76	
77	6) s3c2410_gpio_getirq() should be directly replaceable with the
78	   gpio_to_irq() call.
79	
80	The s3c2410_gpio and gpio_ calls have always operated on the same gpio
81	numberspace, so there is no problem with converting the gpio numbering
82	between the calls.
83	
84	
85	Headers
86	-------
87	
88	  See arch/arm/mach-s3c2410/include/mach/regs-gpio.h for the list
89	  of GPIO pins, and the configuration values for them. This
90	  is included by using #include <mach/regs-gpio.h>
91	
92	  The GPIO management functions are defined in the hardware
93	  header arch/arm/mach-s3c2410/include/mach/hardware.h which can be
94	  included by #include <mach/hardware.h>
95	
96	  A useful amount of documentation can be found in the hardware
97	  header on how the GPIO functions (and others) work.
98	
99	  Whilst a number of these functions do make some checks on what
100	  is passed to them, for speed of use, they may not always ensure
101	  that the user supplied data to them is correct.
102	
103	
104	PIN Numbers
105	-----------
106	
107	  Each pin has an unique number associated with it in regs-gpio.h,
108	  e.g. S3C2410_GPA(0) or S3C2410_GPF(1). These defines are used to tell
109	  the GPIO functions which pin is to be used.
110	
111	  With the conversion to gpiolib, there is no longer a direct conversion
112	  from gpio pin number to register base address as in earlier kernels. This
113	  is due to the number space required for newer SoCs where the later
114	  GPIOs are not contiguous.
115	
116	
117	Configuring a pin
118	-----------------
119	
120	  The following function allows the configuration of a given pin to
121	  be changed.
122	
123	    void s3c_gpio_cfgpin(unsigned int pin, unsigned int function);
124	
125	  e.g.:
126	
127	     s3c_gpio_cfgpin(S3C2410_GPA(0), S3C_GPIO_SFN(1));
128	     s3c_gpio_cfgpin(S3C2410_GPE(8), S3C_GPIO_SFN(2));
129	
130	   which would turn GPA(0) into the lowest Address line A0, and set
131	   GPE(8) to be connected to the SDIO/MMC controller's SDDAT1 line.
132	
133	
134	Reading the current configuration
135	---------------------------------
136	
137	  The current configuration of a pin can be read by using standard
138	  gpiolib function:
139	
140	  s3c_gpio_getcfg(unsigned int pin);
141	
142	  The return value will be from the same set of values which can be
143	  passed to s3c_gpio_cfgpin().
144	
145	
146	Configuring a pull-up resistor
147	------------------------------
148	
149	  A large proportion of the GPIO pins on the S3C2410 can have weak
150	  pull-up resistors enabled. This can be configured by the following
151	  function:
152	
153	    void s3c_gpio_setpull(unsigned int pin, unsigned int to);
154	
155	  Where the to value is S3C_GPIO_PULL_NONE to set the pull-up off,
156	  and S3C_GPIO_PULL_UP to enable the specified pull-up. Any other
157	  values are currently undefined.
158	
159	
160	Getting and setting the state of a PIN
161	--------------------------------------
162	
163	  These calls are now implemented by the relevant gpiolib calls, convert
164	  your board or driver to use gpiolib.
165	
166	
167	Getting the IRQ number associated with a PIN
168	--------------------------------------------
169	
170	  A standard gpiolib function can map the given pin number to an IRQ
171	  number to pass to the IRQ system.
172	
173	   int gpio_to_irq(unsigned int pin);
174	
175	  Note, not all pins have an IRQ.
176	
177	
178	Author
179	-------
180	
181	Ben Dooks, 03 October 2004
182	Copyright 2004 Ben Dooks, Simtec Electronics
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