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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 EST.

1	PINCTRL (PIN CONTROL) subsystem
2	This document outlines the pin control subsystem in Linux
3	
4	This subsystem deals with:
5	
6	- Enumerating and naming controllable pins
7	
8	- Multiplexing of pins, pads, fingers (etc) see below for details
9	
10	- Configuration of pins, pads, fingers (etc), such as software-controlled
11	  biasing and driving mode specific pins, such as pull-up/down, open drain,
12	  load capacitance etc.
13	
14	Top-level interface
15	===================
16	
17	Definition of PIN CONTROLLER:
18	
19	- A pin controller is a piece of hardware, usually a set of registers, that
20	  can control PINs. It may be able to multiplex, bias, set load capacitance,
21	  set drive strength etc for individual pins or groups of pins.
22	
23	Definition of PIN:
24	
25	- PINS are equal to pads, fingers, balls or whatever packaging input or
26	  output line you want to control and these are denoted by unsigned integers
27	  in the range 0..maxpin. This numberspace is local to each PIN CONTROLLER, so
28	  there may be several such number spaces in a system. This pin space may
29	  be sparse - i.e. there may be gaps in the space with numbers where no
30	  pin exists.
31	
32	When a PIN CONTROLLER is instantiated, it will register a descriptor to the
33	pin control framework, and this descriptor contains an array of pin descriptors
34	describing the pins handled by this specific pin controller.
35	
36	Here is an example of a PGA (Pin Grid Array) chip seen from underneath:
37	
38	        A   B   C   D   E   F   G   H
39	
40	   8    o   o   o   o   o   o   o   o
41	
42	   7    o   o   o   o   o   o   o   o
43	
44	   6    o   o   o   o   o   o   o   o
45	
46	   5    o   o   o   o   o   o   o   o
47	
48	   4    o   o   o   o   o   o   o   o
49	
50	   3    o   o   o   o   o   o   o   o
51	
52	   2    o   o   o   o   o   o   o   o
53	
54	   1    o   o   o   o   o   o   o   o
55	
56	To register a pin controller and name all the pins on this package we can do
57	this in our driver:
58	
59	#include <linux/pinctrl/pinctrl.h>
60	
61	const struct pinctrl_pin_desc foo_pins[] = {
62	      PINCTRL_PIN(0, "A8"),
63	      PINCTRL_PIN(1, "B8"),
64	      PINCTRL_PIN(2, "C8"),
65	      ...
66	      PINCTRL_PIN(61, "F1"),
67	      PINCTRL_PIN(62, "G1"),
68	      PINCTRL_PIN(63, "H1"),
69	};
70	
71	static struct pinctrl_desc foo_desc = {
72		.name = "foo",
73		.pins = foo_pins,
74		.npins = ARRAY_SIZE(foo_pins),
75		.maxpin = 63,
76		.owner = THIS_MODULE,
77	};
78	
79	int __init foo_probe(void)
80	{
81		struct pinctrl_dev *pctl;
82	
83		pctl = pinctrl_register(&foo_desc, <PARENT>, NULL);
84		if (!pctl)
85			pr_err("could not register foo pin driver\n");
86	}
87	
88	To enable the pinctrl subsystem and the subgroups for PINMUX and PINCONF and
89	selected drivers, you need to select them from your machine's Kconfig entry,
90	since these are so tightly integrated with the machines they are used on.
91	See for example arch/arm/mach-u300/Kconfig for an example.
92	
93	Pins usually have fancier names than this. You can find these in the dataheet
94	for your chip. Notice that the core pinctrl.h file provides a fancy macro
95	called PINCTRL_PIN() to create the struct entries. As you can see I enumerated
96	the pins from 0 in the upper left corner to 63 in the lower right corner.
97	This enumeration was arbitrarily chosen, in practice you need to think
98	through your numbering system so that it matches the layout of registers
99	and such things in your driver, or the code may become complicated. You must
100	also consider matching of offsets to the GPIO ranges that may be handled by
101	the pin controller.
102	
103	For a padring with 467 pads, as opposed to actual pins, I used an enumeration
104	like this, walking around the edge of the chip, which seems to be industry
105	standard too (all these pads had names, too):
106	
107	
108	     0 ..... 104
109	   466        105
110	     .        .
111	     .        .
112	   358        224
113	    357 .... 225
114	
115	
116	Pin groups
117	==========
118	
119	Many controllers need to deal with groups of pins, so the pin controller
120	subsystem has a mechanism for enumerating groups of pins and retrieving the
121	actual enumerated pins that are part of a certain group.
122	
123	For example, say that we have a group of pins dealing with an SPI interface
124	on { 0, 8, 16, 24 }, and a group of pins dealing with an I2C interface on pins
125	on { 24, 25 }.
126	
127	These two groups are presented to the pin control subsystem by implementing
128	some generic pinctrl_ops like this:
129	
130	#include <linux/pinctrl/pinctrl.h>
131	
132	struct foo_group {
133		const char *name;
134		const unsigned int *pins;
135		const unsigned num_pins;
136	};
137	
138	static const unsigned int spi0_pins[] = { 0, 8, 16, 24 };
139	static const unsigned int i2c0_pins[] = { 24, 25 };
140	
141	static const struct foo_group foo_groups[] = {
142		{
143			.name = "spi0_grp",
144			.pins = spi0_pins,
145			.num_pins = ARRAY_SIZE(spi0_pins),
146		},
147		{
148			.name = "i2c0_grp",
149			.pins = i2c0_pins,
150			.num_pins = ARRAY_SIZE(i2c0_pins),
151		},
152	};
153	
154	
155	static int foo_get_groups_count(struct pinctrl_dev *pctldev)
156	{
157		return ARRAY_SIZE(foo_groups);
158	}
159	
160	static const char *foo_get_group_name(struct pinctrl_dev *pctldev,
161					       unsigned selector)
162	{
163		return foo_groups[selector].name;
164	}
165	
166	static int foo_get_group_pins(struct pinctrl_dev *pctldev, unsigned selector,
167				       unsigned ** const pins,
168				       unsigned * const num_pins)
169	{
170		*pins = (unsigned *) foo_groups[selector].pins;
171		*num_pins = foo_groups[selector].num_pins;
172		return 0;
173	}
174	
175	static struct pinctrl_ops foo_pctrl_ops = {
176		.get_groups_count = foo_get_groups_count,
177		.get_group_name = foo_get_group_name,
178		.get_group_pins = foo_get_group_pins,
179	};
180	
181	
182	static struct pinctrl_desc foo_desc = {
183	       ...
184	       .pctlops = &foo_pctrl_ops,
185	};
186	
187	The pin control subsystem will call the .get_groups_count() function to
188	determine total number of legal selectors, then it will call the other functions
189	to retrieve the name and pins of the group. Maintaining the data structure of
190	the groups is up to the driver, this is just a simple example - in practice you
191	may need more entries in your group structure, for example specific register
192	ranges associated with each group and so on.
193	
194	
195	Pin configuration
196	=================
197	
198	Pins can sometimes be software-configured in an various ways, mostly related
199	to their electronic properties when used as inputs or outputs. For example you
200	may be able to make an output pin high impedance, or "tristate" meaning it is
201	effectively disconnected. You may be able to connect an input pin to VDD or GND
202	using a certain resistor value - pull up and pull down - so that the pin has a
203	stable value when nothing is driving the rail it is connected to, or when it's
204	unconnected.
205	
206	Pin configuration can be programmed by adding configuration entries into the
207	mapping table; see section "Board/machine configuration" below.
208	
209	The format and meaning of the configuration parameter, PLATFORM_X_PULL_UP
210	above, is entirely defined by the pin controller driver.
211	
212	The pin configuration driver implements callbacks for changing pin
213	configuration in the pin controller ops like this:
214	
215	#include <linux/pinctrl/pinctrl.h>
216	#include <linux/pinctrl/pinconf.h>
217	#include "platform_x_pindefs.h"
218	
219	static int foo_pin_config_get(struct pinctrl_dev *pctldev,
220			    unsigned offset,
221			    unsigned long *config)
222	{
223		struct my_conftype conf;
224	
225		... Find setting for pin @ offset ...
226	
227		*config = (unsigned long) conf;
228	}
229	
230	static int foo_pin_config_set(struct pinctrl_dev *pctldev,
231			    unsigned offset,
232			    unsigned long config)
233	{
234		struct my_conftype *conf = (struct my_conftype *) config;
235	
236		switch (conf) {
237			case PLATFORM_X_PULL_UP:
238			...
239			}
240		}
241	}
242	
243	static int foo_pin_config_group_get (struct pinctrl_dev *pctldev,
244			    unsigned selector,
245			    unsigned long *config)
246	{
247		...
248	}
249	
250	static int foo_pin_config_group_set (struct pinctrl_dev *pctldev,
251			    unsigned selector,
252			    unsigned long config)
253	{
254		...
255	}
256	
257	static struct pinconf_ops foo_pconf_ops = {
258		.pin_config_get = foo_pin_config_get,
259		.pin_config_set = foo_pin_config_set,
260		.pin_config_group_get = foo_pin_config_group_get,
261		.pin_config_group_set = foo_pin_config_group_set,
262	};
263	
264	/* Pin config operations are handled by some pin controller */
265	static struct pinctrl_desc foo_desc = {
266		...
267		.confops = &foo_pconf_ops,
268	};
269	
270	Since some controllers have special logic for handling entire groups of pins
271	they can exploit the special whole-group pin control function. The
272	pin_config_group_set() callback is allowed to return the error code -EAGAIN,
273	for groups it does not want to handle, or if it just wants to do some
274	group-level handling and then fall through to iterate over all pins, in which
275	case each individual pin will be treated by separate pin_config_set() calls as
276	well.
277	
278	
279	Interaction with the GPIO subsystem
280	===================================
281	
282	The GPIO drivers may want to perform operations of various types on the same
283	physical pins that are also registered as pin controller pins.
284	
285	First and foremost, the two subsystems can be used as completely orthogonal,
286	see the section named "pin control requests from drivers" and
287	"drivers needing both pin control and GPIOs" below for details. But in some
288	situations a cross-subsystem mapping between pins and GPIOs is needed.
289	
290	Since the pin controller subsystem have its pinspace local to the pin
291	controller we need a mapping so that the pin control subsystem can figure out
292	which pin controller handles control of a certain GPIO pin. Since a single
293	pin controller may be muxing several GPIO ranges (typically SoCs that have
294	one set of pins but internally several GPIO silicon blocks, each modelled as
295	a struct gpio_chip) any number of GPIO ranges can be added to a pin controller
296	instance like this:
297	
298	struct gpio_chip chip_a;
299	struct gpio_chip chip_b;
300	
301	static struct pinctrl_gpio_range gpio_range_a = {
302		.name = "chip a",
303		.id = 0,
304		.base = 32,
305		.pin_base = 32,
306		.npins = 16,
307		.gc = &chip_a;
308	};
309	
310	static struct pinctrl_gpio_range gpio_range_b = {
311		.name = "chip b",
312		.id = 0,
313		.base = 48,
314		.pin_base = 64,
315		.npins = 8,
316		.gc = &chip_b;
317	};
318	
319	{
320		struct pinctrl_dev *pctl;
321		...
322		pinctrl_add_gpio_range(pctl, &gpio_range_a);
323		pinctrl_add_gpio_range(pctl, &gpio_range_b);
324	}
325	
326	So this complex system has one pin controller handling two different
327	GPIO chips. "chip a" has 16 pins and "chip b" has 8 pins. The "chip a" and
328	"chip b" have different .pin_base, which means a start pin number of the
329	GPIO range.
330	
331	The GPIO range of "chip a" starts from the GPIO base of 32 and actual
332	pin range also starts from 32. However "chip b" has different starting
333	offset for the GPIO range and pin range. The GPIO range of "chip b" starts
334	from GPIO number 48, while the pin range of "chip b" starts from 64.
335	
336	We can convert a gpio number to actual pin number using this "pin_base".
337	They are mapped in the global GPIO pin space at:
338	
339	chip a:
340	 - GPIO range : [32 .. 47]
341	 - pin range  : [32 .. 47]
342	chip b:
343	 - GPIO range : [48 .. 55]
344	 - pin range  : [64 .. 71]
345	
346	The above examples assume the mapping between the GPIOs and pins is
347	linear. If the mapping is sparse or haphazard, an array of arbitrary pin
348	numbers can be encoded in the range like this:
349	
350	static const unsigned range_pins[] = { 14, 1, 22, 17, 10, 8, 6, 2 };
351	
352	static struct pinctrl_gpio_range gpio_range = {
353		.name = "chip",
354		.id = 0,
355		.base = 32,
356		.pins = &range_pins,
357		.npins = ARRAY_SIZE(range_pins),
358		.gc = &chip;
359	};
360	
361	In this case the pin_base property will be ignored. If the name of a pin
362	group is known, the pins and npins elements of the above structure can be
363	initialised using the function pinctrl_get_group_pins(), e.g. for pin
364	group "foo":
365	
366	pinctrl_get_group_pins(pctl, "foo", &gpio_range.pins, &gpio_range.npins);
367	
368	When GPIO-specific functions in the pin control subsystem are called, these
369	ranges will be used to look up the appropriate pin controller by inspecting
370	and matching the pin to the pin ranges across all controllers. When a
371	pin controller handling the matching range is found, GPIO-specific functions
372	will be called on that specific pin controller.
373	
374	For all functionalities dealing with pin biasing, pin muxing etc, the pin
375	controller subsystem will look up the corresponding pin number from the passed
376	in gpio number, and use the range's internals to retrive a pin number. After
377	that, the subsystem passes it on to the pin control driver, so the driver
378	will get an pin number into its handled number range. Further it is also passed
379	the range ID value, so that the pin controller knows which range it should
380	deal with.
381	
382	Calling pinctrl_add_gpio_range from pinctrl driver is DEPRECATED. Please see
383	section 2.1 of Documentation/devicetree/bindings/gpio/gpio.txt on how to bind
384	pinctrl and gpio drivers.
385	
386	
387	PINMUX interfaces
388	=================
389	
390	These calls use the pinmux_* naming prefix.  No other calls should use that
391	prefix.
392	
393	
394	What is pinmuxing?
395	==================
396	
397	PINMUX, also known as padmux, ballmux, alternate functions or mission modes
398	is a way for chip vendors producing some kind of electrical packages to use
399	a certain physical pin (ball, pad, finger, etc) for multiple mutually exclusive
400	functions, depending on the application. By "application" in this context
401	we usually mean a way of soldering or wiring the package into an electronic
402	system, even though the framework makes it possible to also change the function
403	at runtime.
404	
405	Here is an example of a PGA (Pin Grid Array) chip seen from underneath:
406	
407	        A   B   C   D   E   F   G   H
408	      +---+
409	   8  | o | o   o   o   o   o   o   o
410	      |   |
411	   7  | o | o   o   o   o   o   o   o
412	      |   |
413	   6  | o | o   o   o   o   o   o   o
414	      +---+---+
415	   5  | o | o | o   o   o   o   o   o
416	      +---+---+               +---+
417	   4    o   o   o   o   o   o | o | o
418	                              |   |
419	   3    o   o   o   o   o   o | o | o
420	                              |   |
421	   2    o   o   o   o   o   o | o | o
422	      +-------+-------+-------+---+---+
423	   1  | o   o | o   o | o   o | o | o |
424	      +-------+-------+-------+---+---+
425	
426	This is not tetris. The game to think of is chess. Not all PGA/BGA packages
427	are chessboard-like, big ones have "holes" in some arrangement according to
428	different design patterns, but we're using this as a simple example. Of the
429	pins you see some will be taken by things like a few VCC and GND to feed power
430	to the chip, and quite a few will be taken by large ports like an external
431	memory interface. The remaining pins will often be subject to pin multiplexing.
432	
433	The example 8x8 PGA package above will have pin numbers 0 thru 63 assigned to
434	its physical pins. It will name the pins { A1, A2, A3 ... H6, H7, H8 } using
435	pinctrl_register_pins() and a suitable data set as shown earlier.
436	
437	In this 8x8 BGA package the pins { A8, A7, A6, A5 } can be used as an SPI port
438	(these are four pins: CLK, RXD, TXD, FRM). In that case, pin B5 can be used as
439	some general-purpose GPIO pin. However, in another setting, pins { A5, B5 } can
440	be used as an I2C port (these are just two pins: SCL, SDA). Needless to say,
441	we cannot use the SPI port and I2C port at the same time. However in the inside
442	of the package the silicon performing the SPI logic can alternatively be routed
443	out on pins { G4, G3, G2, G1 }.
444	
445	On the botton row at { A1, B1, C1, D1, E1, F1, G1, H1 } we have something
446	special - it's an external MMC bus that can be 2, 4 or 8 bits wide, and it will
447	consume 2, 4 or 8 pins respectively, so either { A1, B1 } are taken or
448	{ A1, B1, C1, D1 } or all of them. If we use all 8 bits, we cannot use the SPI
449	port on pins { G4, G3, G2, G1 } of course.
450	
451	This way the silicon blocks present inside the chip can be multiplexed "muxed"
452	out on different pin ranges. Often contemporary SoC (systems on chip) will
453	contain several I2C, SPI, SDIO/MMC, etc silicon blocks that can be routed to
454	different pins by pinmux settings.
455	
456	Since general-purpose I/O pins (GPIO) are typically always in shortage, it is
457	common to be able to use almost any pin as a GPIO pin if it is not currently
458	in use by some other I/O port.
459	
460	
461	Pinmux conventions
462	==================
463	
464	The purpose of the pinmux functionality in the pin controller subsystem is to
465	abstract and provide pinmux settings to the devices you choose to instantiate
466	in your machine configuration. It is inspired by the clk, GPIO and regulator
467	subsystems, so devices will request their mux setting, but it's also possible
468	to request a single pin for e.g. GPIO.
469	
470	Definitions:
471	
472	- FUNCTIONS can be switched in and out by a driver residing with the pin
473	  control subsystem in the drivers/pinctrl/* directory of the kernel. The
474	  pin control driver knows the possible functions. In the example above you can
475	  identify three pinmux functions, one for spi, one for i2c and one for mmc.
476	
477	- FUNCTIONS are assumed to be enumerable from zero in a one-dimensional array.
478	  In this case the array could be something like: { spi0, i2c0, mmc0 }
479	  for the three available functions.
480	
481	- FUNCTIONS have PIN GROUPS as defined on the generic level - so a certain
482	  function is *always* associated with a certain set of pin groups, could
483	  be just a single one, but could also be many. In the example above the
484	  function i2c is associated with the pins { A5, B5 }, enumerated as
485	  { 24, 25 } in the controller pin space.
486	
487	  The Function spi is associated with pin groups { A8, A7, A6, A5 }
488	  and { G4, G3, G2, G1 }, which are enumerated as { 0, 8, 16, 24 } and
489	  { 38, 46, 54, 62 } respectively.
490	
491	  Group names must be unique per pin controller, no two groups on the same
492	  controller may have the same name.
493	
494	- The combination of a FUNCTION and a PIN GROUP determine a certain function
495	  for a certain set of pins. The knowledge of the functions and pin groups
496	  and their machine-specific particulars are kept inside the pinmux driver,
497	  from the outside only the enumerators are known, and the driver core can:
498	
499	  - Request the name of a function with a certain selector (>= 0)
500	  - A list of groups associated with a certain function
501	  - Request that a certain group in that list to be activated for a certain
502	    function
503	
504	  As already described above, pin groups are in turn self-descriptive, so
505	  the core will retrieve the actual pin range in a certain group from the
506	  driver.
507	
508	- FUNCTIONS and GROUPS on a certain PIN CONTROLLER are MAPPED to a certain
509	  device by the board file, device tree or similar machine setup configuration
510	  mechanism, similar to how regulators are connected to devices, usually by
511	  name. Defining a pin controller, function and group thus uniquely identify
512	  the set of pins to be used by a certain device. (If only one possible group
513	  of pins is available for the function, no group name need to be supplied -
514	  the core will simply select the first and only group available.)
515	
516	  In the example case we can define that this particular machine shall
517	  use device spi0 with pinmux function fspi0 group gspi0 and i2c0 on function
518	  fi2c0 group gi2c0, on the primary pin controller, we get mappings
519	  like these:
520	
521	  {
522	    {"map-spi0", spi0, pinctrl0, fspi0, gspi0},
523	    {"map-i2c0", i2c0, pinctrl0, fi2c0, gi2c0}
524	  }
525	
526	  Every map must be assigned a state name, pin controller, device and
527	  function. The group is not compulsory - if it is omitted the first group
528	  presented by the driver as applicable for the function will be selected,
529	  which is useful for simple cases.
530	
531	  It is possible to map several groups to the same combination of device,
532	  pin controller and function. This is for cases where a certain function on
533	  a certain pin controller may use different sets of pins in different
534	  configurations.
535	
536	- PINS for a certain FUNCTION using a certain PIN GROUP on a certain
537	  PIN CONTROLLER are provided on a first-come first-serve basis, so if some
538	  other device mux setting or GPIO pin request has already taken your physical
539	  pin, you will be denied the use of it. To get (activate) a new setting, the
540	  old one has to be put (deactivated) first.
541	
542	Sometimes the documentation and hardware registers will be oriented around
543	pads (or "fingers") rather than pins - these are the soldering surfaces on the
544	silicon inside the package, and may or may not match the actual number of
545	pins/balls underneath the capsule. Pick some enumeration that makes sense to
546	you. Define enumerators only for the pins you can control if that makes sense.
547	
548	Assumptions:
549	
550	We assume that the number of possible function maps to pin groups is limited by
551	the hardware. I.e. we assume that there is no system where any function can be
552	mapped to any pin, like in a phone exchange. So the available pins groups for
553	a certain function will be limited to a few choices (say up to eight or so),
554	not hundreds or any amount of choices. This is the characteristic we have found
555	by inspecting available pinmux hardware, and a necessary assumption since we
556	expect pinmux drivers to present *all* possible function vs pin group mappings
557	to the subsystem.
558	
559	
560	Pinmux drivers
561	==============
562	
563	The pinmux core takes care of preventing conflicts on pins and calling
564	the pin controller driver to execute different settings.
565	
566	It is the responsibility of the pinmux driver to impose further restrictions
567	(say for example infer electronic limitations due to load etc) to determine
568	whether or not the requested function can actually be allowed, and in case it
569	is possible to perform the requested mux setting, poke the hardware so that
570	this happens.
571	
572	Pinmux drivers are required to supply a few callback functions, some are
573	optional. Usually the enable() and disable() functions are implemented,
574	writing values into some certain registers to activate a certain mux setting
575	for a certain pin.
576	
577	A simple driver for the above example will work by setting bits 0, 1, 2, 3 or 4
578	into some register named MUX to select a certain function with a certain
579	group of pins would work something like this:
580	
581	#include <linux/pinctrl/pinctrl.h>
582	#include <linux/pinctrl/pinmux.h>
583	
584	struct foo_group {
585		const char *name;
586		const unsigned int *pins;
587		const unsigned num_pins;
588	};
589	
590	static const unsigned spi0_0_pins[] = { 0, 8, 16, 24 };
591	static const unsigned spi0_1_pins[] = { 38, 46, 54, 62 };
592	static const unsigned i2c0_pins[] = { 24, 25 };
593	static const unsigned mmc0_1_pins[] = { 56, 57 };
594	static const unsigned mmc0_2_pins[] = { 58, 59 };
595	static const unsigned mmc0_3_pins[] = { 60, 61, 62, 63 };
596	
597	static const struct foo_group foo_groups[] = {
598		{
599			.name = "spi0_0_grp",
600			.pins = spi0_0_pins,
601			.num_pins = ARRAY_SIZE(spi0_0_pins),
602		},
603		{
604			.name = "spi0_1_grp",
605			.pins = spi0_1_pins,
606			.num_pins = ARRAY_SIZE(spi0_1_pins),
607		},
608		{
609			.name = "i2c0_grp",
610			.pins = i2c0_pins,
611			.num_pins = ARRAY_SIZE(i2c0_pins),
612		},
613		{
614			.name = "mmc0_1_grp",
615			.pins = mmc0_1_pins,
616			.num_pins = ARRAY_SIZE(mmc0_1_pins),
617		},
618		{
619			.name = "mmc0_2_grp",
620			.pins = mmc0_2_pins,
621			.num_pins = ARRAY_SIZE(mmc0_2_pins),
622		},
623		{
624			.name = "mmc0_3_grp",
625			.pins = mmc0_3_pins,
626			.num_pins = ARRAY_SIZE(mmc0_3_pins),
627		},
628	};
629	
630	
631	static int foo_get_groups_count(struct pinctrl_dev *pctldev)
632	{
633		return ARRAY_SIZE(foo_groups);
634	}
635	
636	static const char *foo_get_group_name(struct pinctrl_dev *pctldev,
637					       unsigned selector)
638	{
639		return foo_groups[selector].name;
640	}
641	
642	static int foo_get_group_pins(struct pinctrl_dev *pctldev, unsigned selector,
643				       unsigned ** const pins,
644				       unsigned * const num_pins)
645	{
646		*pins = (unsigned *) foo_groups[selector].pins;
647		*num_pins = foo_groups[selector].num_pins;
648		return 0;
649	}
650	
651	static struct pinctrl_ops foo_pctrl_ops = {
652		.get_groups_count = foo_get_groups_count,
653		.get_group_name = foo_get_group_name,
654		.get_group_pins = foo_get_group_pins,
655	};
656	
657	struct foo_pmx_func {
658		const char *name;
659		const char * const *groups;
660		const unsigned num_groups;
661	};
662	
663	static const char * const spi0_groups[] = { "spi0_0_grp", "spi0_1_grp" };
664	static const char * const i2c0_groups[] = { "i2c0_grp" };
665	static const char * const mmc0_groups[] = { "mmc0_1_grp", "mmc0_2_grp",
666						"mmc0_3_grp" };
667	
668	static const struct foo_pmx_func foo_functions[] = {
669		{
670			.name = "spi0",
671			.groups = spi0_groups,
672			.num_groups = ARRAY_SIZE(spi0_groups),
673		},
674		{
675			.name = "i2c0",
676			.groups = i2c0_groups,
677			.num_groups = ARRAY_SIZE(i2c0_groups),
678		},
679		{
680			.name = "mmc0",
681			.groups = mmc0_groups,
682			.num_groups = ARRAY_SIZE(mmc0_groups),
683		},
684	};
685	
686	int foo_get_functions_count(struct pinctrl_dev *pctldev)
687	{
688		return ARRAY_SIZE(foo_functions);
689	}
690	
691	const char *foo_get_fname(struct pinctrl_dev *pctldev, unsigned selector)
692	{
693		return foo_functions[selector].name;
694	}
695	
696	static int foo_get_groups(struct pinctrl_dev *pctldev, unsigned selector,
697				  const char * const **groups,
698				  unsigned * const num_groups)
699	{
700		*groups = foo_functions[selector].groups;
701		*num_groups = foo_functions[selector].num_groups;
702		return 0;
703	}
704	
705	int foo_enable(struct pinctrl_dev *pctldev, unsigned selector,
706			unsigned group)
707	{
708		u8 regbit = (1 << selector + group);
709	
710		writeb((readb(MUX)|regbit), MUX)
711		return 0;
712	}
713	
714	void foo_disable(struct pinctrl_dev *pctldev, unsigned selector,
715			unsigned group)
716	{
717		u8 regbit = (1 << selector + group);
718	
719		writeb((readb(MUX) & ~(regbit)), MUX)
720		return 0;
721	}
722	
723	struct pinmux_ops foo_pmxops = {
724		.get_functions_count = foo_get_functions_count,
725		.get_function_name = foo_get_fname,
726		.get_function_groups = foo_get_groups,
727		.enable = foo_enable,
728		.disable = foo_disable,
729	};
730	
731	/* Pinmux operations are handled by some pin controller */
732	static struct pinctrl_desc foo_desc = {
733		...
734		.pctlops = &foo_pctrl_ops,
735		.pmxops = &foo_pmxops,
736	};
737	
738	In the example activating muxing 0 and 1 at the same time setting bits
739	0 and 1, uses one pin in common so they would collide.
740	
741	The beauty of the pinmux subsystem is that since it keeps track of all
742	pins and who is using them, it will already have denied an impossible
743	request like that, so the driver does not need to worry about such
744	things - when it gets a selector passed in, the pinmux subsystem makes
745	sure no other device or GPIO assignment is already using the selected
746	pins. Thus bits 0 and 1 in the control register will never be set at the
747	same time.
748	
749	All the above functions are mandatory to implement for a pinmux driver.
750	
751	
752	Pin control interaction with the GPIO subsystem
753	===============================================
754	
755	Note that the following implies that the use case is to use a certain pin
756	from the Linux kernel using the API in <linux/gpio.h> with gpio_request()
757	and similar functions. There are cases where you may be using something
758	that your datasheet calls "GPIO mode" but actually is just an electrical
759	configuration for a certain device. See the section below named
760	"GPIO mode pitfalls" for more details on this scenario.
761	
762	The public pinmux API contains two functions named pinctrl_request_gpio()
763	and pinctrl_free_gpio(). These two functions shall *ONLY* be called from
764	gpiolib-based drivers as part of their gpio_request() and
765	gpio_free() semantics. Likewise the pinctrl_gpio_direction_[input|output]
766	shall only be called from within respective gpio_direction_[input|output]
767	gpiolib implementation.
768	
769	NOTE that platforms and individual drivers shall *NOT* request GPIO pins to be
770	controlled e.g. muxed in. Instead, implement a proper gpiolib driver and have
771	that driver request proper muxing and other control for its pins.
772	
773	The function list could become long, especially if you can convert every
774	individual pin into a GPIO pin independent of any other pins, and then try
775	the approach to define every pin as a function.
776	
777	In this case, the function array would become 64 entries for each GPIO
778	setting and then the device functions.
779	
780	For this reason there are two functions a pin control driver can implement
781	to enable only GPIO on an individual pin: .gpio_request_enable() and
782	.gpio_disable_free().
783	
784	This function will pass in the affected GPIO range identified by the pin
785	controller core, so you know which GPIO pins are being affected by the request
786	operation.
787	
788	If your driver needs to have an indication from the framework of whether the
789	GPIO pin shall be used for input or output you can implement the
790	.gpio_set_direction() function. As described this shall be called from the
791	gpiolib driver and the affected GPIO range, pin offset and desired direction
792	will be passed along to this function.
793	
794	Alternatively to using these special functions, it is fully allowed to use
795	named functions for each GPIO pin, the pinctrl_request_gpio() will attempt to
796	obtain the function "gpioN" where "N" is the global GPIO pin number if no
797	special GPIO-handler is registered.
798	
799	
800	GPIO mode pitfalls
801	==================
802	
803	Due to the naming conventions used by hardware engineers, where "GPIO"
804	is taken to mean different things than what the kernel does, the developer
805	may be confused by a datasheet talking about a pin being possible to set
806	into "GPIO mode". It appears that what hardware engineers mean with
807	"GPIO mode" is not necessarily the use case that is implied in the kernel
808	interface <linux/gpio.h>: a pin that you grab from kernel code and then
809	either listen for input or drive high/low to assert/deassert some
810	external line.
811	
812	Rather hardware engineers think that "GPIO mode" means that you can
813	software-control a few electrical properties of the pin that you would
814	not be able to control if the pin was in some other mode, such as muxed in
815	for a device.
816	
817	The GPIO portions of a pin and its relation to a certain pin controller
818	configuration and muxing logic can be constructed in several ways. Here
819	are two examples:
820	
821	(A)
822	                       pin config
823	                       logic regs
824	                       |               +- SPI
825	     Physical pins --- pad --- pinmux -+- I2C
826	                               |       +- mmc
827	                               |       +- GPIO
828	                               pin
829	                               multiplex
830	                               logic regs
831	
832	Here some electrical properties of the pin can be configured no matter
833	whether the pin is used for GPIO or not. If you multiplex a GPIO onto a
834	pin, you can also drive it high/low from "GPIO" registers.
835	Alternatively, the pin can be controlled by a certain peripheral, while
836	still applying desired pin config properties. GPIO functionality is thus
837	orthogonal to any other device using the pin.
838	
839	In this arrangement the registers for the GPIO portions of the pin controller,
840	or the registers for the GPIO hardware module are likely to reside in a
841	separate memory range only intended for GPIO driving, and the register
842	range dealing with pin config and pin multiplexing get placed into a
843	different memory range and a separate section of the data sheet.
844	
845	(B)
846	
847	                       pin config
848	                       logic regs
849	                       |               +- SPI
850	     Physical pins --- pad --- pinmux -+- I2C
851	                       |       |       +- mmc
852	                       |       |
853	                       GPIO    pin
854	                               multiplex
855	                               logic regs
856	
857	In this arrangement, the GPIO functionality can always be enabled, such that
858	e.g. a GPIO input can be used to "spy" on the SPI/I2C/MMC signal while it is
859	pulsed out. It is likely possible to disrupt the traffic on the pin by doing
860	wrong things on the GPIO block, as it is never really disconnected. It is
861	possible that the GPIO, pin config and pin multiplex registers are placed into
862	the same memory range and the same section of the data sheet, although that
863	need not be the case.
864	
865	From a kernel point of view, however, these are different aspects of the
866	hardware and shall be put into different subsystems:
867	
868	- Registers (or fields within registers) that control electrical
869	  properties of the pin such as biasing and drive strength should be
870	  exposed through the pinctrl subsystem, as "pin configuration" settings.
871	
872	- Registers (or fields within registers) that control muxing of signals
873	  from various other HW blocks (e.g. I2C, MMC, or GPIO) onto pins should
874	  be exposed through the pinctrl subssytem, as mux functions.
875	
876	- Registers (or fields within registers) that control GPIO functionality
877	  such as setting a GPIO's output value, reading a GPIO's input value, or
878	  setting GPIO pin direction should be exposed through the GPIO subsystem,
879	  and if they also support interrupt capabilities, through the irqchip
880	  abstraction.
881	
882	Depending on the exact HW register design, some functions exposed by the
883	GPIO subsystem may call into the pinctrl subsystem in order to
884	co-ordinate register settings across HW modules. In particular, this may
885	be needed for HW with separate GPIO and pin controller HW modules, where
886	e.g. GPIO direction is determined by a register in the pin controller HW
887	module rather than the GPIO HW module.
888	
889	Electrical properties of the pin such as biasing and drive strength
890	may be placed at some pin-specific register in all cases or as part
891	of the GPIO register in case (B) especially. This doesn't mean that such
892	properties necessarily pertain to what the Linux kernel calls "GPIO".
893	
894	Example: a pin is usually muxed in to be used as a UART TX line. But during
895	system sleep, we need to put this pin into "GPIO mode" and ground it.
896	
897	If you make a 1-to-1 map to the GPIO subsystem for this pin, you may start
898	to think that you need to come up with something real complex, that the
899	pin shall be used for UART TX and GPIO at the same time, that you will grab
900	a pin control handle and set it to a certain state to enable UART TX to be
901	muxed in, then twist it over to GPIO mode and use gpio_direction_output()
902	to drive it low during sleep, then mux it over to UART TX again when you
903	wake up and maybe even gpio_request/gpio_free as part of this cycle. This
904	all gets very complicated.
905	
906	The solution is to not think that what the datasheet calls "GPIO mode"
907	has to be handled by the <linux/gpio.h> interface. Instead view this as
908	a certain pin config setting. Look in e.g. <linux/pinctrl/pinconf-generic.h>
909	and you find this in the documentation:
910	
911	  PIN_CONFIG_OUTPUT: this will configure the pin in output, use argument
912	     1 to indicate high level, argument 0 to indicate low level.
913	
914	So it is perfectly possible to push a pin into "GPIO mode" and drive the
915	line low as part of the usual pin control map. So for example your UART
916	driver may look like this:
917	
918	#include <linux/pinctrl/consumer.h>
919	
920	struct pinctrl          *pinctrl;
921	struct pinctrl_state    *pins_default;
922	struct pinctrl_state    *pins_sleep;
923	
924	pins_default = pinctrl_lookup_state(uap->pinctrl, PINCTRL_STATE_DEFAULT);
925	pins_sleep = pinctrl_lookup_state(uap->pinctrl, PINCTRL_STATE_SLEEP);
926	
927	/* Normal mode */
928	retval = pinctrl_select_state(pinctrl, pins_default);
929	/* Sleep mode */
930	retval = pinctrl_select_state(pinctrl, pins_sleep);
931	
932	And your machine configuration may look like this:
933	--------------------------------------------------
934	
935	static unsigned long uart_default_mode[] = {
936	    PIN_CONF_PACKED(PIN_CONFIG_DRIVE_PUSH_PULL, 0),
937	};
938	
939	static unsigned long uart_sleep_mode[] = {
940	    PIN_CONF_PACKED(PIN_CONFIG_OUTPUT, 0),
941	};
942	
943	static struct pinctrl_map pinmap[] __initdata = {
944	    PIN_MAP_MUX_GROUP("uart", PINCTRL_STATE_DEFAULT, "pinctrl-foo",
945	                      "u0_group", "u0"),
946	    PIN_MAP_CONFIGS_PIN("uart", PINCTRL_STATE_DEFAULT, "pinctrl-foo",
947	                        "UART_TX_PIN", uart_default_mode),
948	    PIN_MAP_MUX_GROUP("uart", PINCTRL_STATE_SLEEP, "pinctrl-foo",
949	                      "u0_group", "gpio-mode"),
950	    PIN_MAP_CONFIGS_PIN("uart", PINCTRL_STATE_SLEEP, "pinctrl-foo",
951	                        "UART_TX_PIN", uart_sleep_mode),
952	};
953	
954	foo_init(void) {
955	    pinctrl_register_mappings(pinmap, ARRAY_SIZE(pinmap));
956	}
957	
958	Here the pins we want to control are in the "u0_group" and there is some
959	function called "u0" that can be enabled on this group of pins, and then
960	everything is UART business as usual. But there is also some function
961	named "gpio-mode" that can be mapped onto the same pins to move them into
962	GPIO mode.
963	
964	This will give the desired effect without any bogus interaction with the
965	GPIO subsystem. It is just an electrical configuration used by that device
966	when going to sleep, it might imply that the pin is set into something the
967	datasheet calls "GPIO mode" but that is not the point: it is still used
968	by that UART device to control the pins that pertain to that very UART
969	driver, putting them into modes needed by the UART. GPIO in the Linux
970	kernel sense are just some 1-bit line, and is a different use case.
971	
972	How the registers are poked to attain the push/pull and output low
973	configuration and the muxing of the "u0" or "gpio-mode" group onto these
974	pins is a question for the driver.
975	
976	Some datasheets will be more helpful and refer to the "GPIO mode" as
977	"low power mode" rather than anything to do with GPIO. This often means
978	the same thing electrically speaking, but in this latter case the
979	software engineers will usually quickly identify that this is some
980	specific muxing/configuration rather than anything related to the GPIO
981	API.
982	
983	
984	Board/machine configuration
985	==================================
986	
987	Boards and machines define how a certain complete running system is put
988	together, including how GPIOs and devices are muxed, how regulators are
989	constrained and how the clock tree looks. Of course pinmux settings are also
990	part of this.
991	
992	A pin controller configuration for a machine looks pretty much like a simple
993	regulator configuration, so for the example array above we want to enable i2c
994	and spi on the second function mapping:
995	
996	#include <linux/pinctrl/machine.h>
997	
998	static const struct pinctrl_map mapping[] __initconst = {
999		{
1000			.dev_name = "foo-spi.0",
1001			.name = PINCTRL_STATE_DEFAULT,
1002			.type = PIN_MAP_TYPE_MUX_GROUP,
1003			.ctrl_dev_name = "pinctrl-foo",
1004			.data.mux.function = "spi0",
1005		},
1006		{
1007			.dev_name = "foo-i2c.0",
1008			.name = PINCTRL_STATE_DEFAULT,
1009			.type = PIN_MAP_TYPE_MUX_GROUP,
1010			.ctrl_dev_name = "pinctrl-foo",
1011			.data.mux.function = "i2c0",
1012		},
1013		{
1014			.dev_name = "foo-mmc.0",
1015			.name = PINCTRL_STATE_DEFAULT,
1016			.type = PIN_MAP_TYPE_MUX_GROUP,
1017			.ctrl_dev_name = "pinctrl-foo",
1018			.data.mux.function = "mmc0",
1019		},
1020	};
1021	
1022	The dev_name here matches to the unique device name that can be used to look
1023	up the device struct (just like with clockdev or regulators). The function name
1024	must match a function provided by the pinmux driver handling this pin range.
1025	
1026	As you can see we may have several pin controllers on the system and thus
1027	we need to specify which one of them that contain the functions we wish
1028	to map.
1029	
1030	You register this pinmux mapping to the pinmux subsystem by simply:
1031	
1032	       ret = pinctrl_register_mappings(mapping, ARRAY_SIZE(mapping));
1033	
1034	Since the above construct is pretty common there is a helper macro to make
1035	it even more compact which assumes you want to use pinctrl-foo and position
1036	0 for mapping, for example:
1037	
1038	static struct pinctrl_map mapping[] __initdata = {
1039		PIN_MAP_MUX_GROUP("foo-i2c.o", PINCTRL_STATE_DEFAULT, "pinctrl-foo", NULL, "i2c0"),
1040	};
1041	
1042	The mapping table may also contain pin configuration entries. It's common for
1043	each pin/group to have a number of configuration entries that affect it, so
1044	the table entries for configuration reference an array of config parameters
1045	and values. An example using the convenience macros is shown below:
1046	
1047	static unsigned long i2c_grp_configs[] = {
1048		FOO_PIN_DRIVEN,
1049		FOO_PIN_PULLUP,
1050	};
1051	
1052	static unsigned long i2c_pin_configs[] = {
1053		FOO_OPEN_COLLECTOR,
1054		FOO_SLEW_RATE_SLOW,
1055	};
1056	
1057	static struct pinctrl_map mapping[] __initdata = {
1058		PIN_MAP_MUX_GROUP("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0", "i2c0"),
1059		PIN_MAP_CONFIGS_GROUP("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0", i2c_grp_configs),
1060		PIN_MAP_CONFIGS_PIN("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0scl", i2c_pin_configs),
1061		PIN_MAP_CONFIGS_PIN("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0sda", i2c_pin_configs),
1062	};
1063	
1064	Finally, some devices expect the mapping table to contain certain specific
1065	named states. When running on hardware that doesn't need any pin controller
1066	configuration, the mapping table must still contain those named states, in
1067	order to explicitly indicate that the states were provided and intended to
1068	be empty. Table entry macro PIN_MAP_DUMMY_STATE serves the purpose of defining
1069	a named state without causing any pin controller to be programmed:
1070	
1071	static struct pinctrl_map mapping[] __initdata = {
1072		PIN_MAP_DUMMY_STATE("foo-i2c.0", PINCTRL_STATE_DEFAULT),
1073	};
1074	
1075	
1076	Complex mappings
1077	================
1078	
1079	As it is possible to map a function to different groups of pins an optional
1080	.group can be specified like this:
1081	
1082	...
1083	{
1084		.dev_name = "foo-spi.0",
1085		.name = "spi0-pos-A",
1086		.type = PIN_MAP_TYPE_MUX_GROUP,
1087		.ctrl_dev_name = "pinctrl-foo",
1088		.function = "spi0",
1089		.group = "spi0_0_grp",
1090	},
1091	{
1092		.dev_name = "foo-spi.0",
1093		.name = "spi0-pos-B",
1094		.type = PIN_MAP_TYPE_MUX_GROUP,
1095		.ctrl_dev_name = "pinctrl-foo",
1096		.function = "spi0",
1097		.group = "spi0_1_grp",
1098	},
1099	...
1100	
1101	This example mapping is used to switch between two positions for spi0 at
1102	runtime, as described further below under the heading "Runtime pinmuxing".
1103	
1104	Further it is possible for one named state to affect the muxing of several
1105	groups of pins, say for example in the mmc0 example above, where you can
1106	additively expand the mmc0 bus from 2 to 4 to 8 pins. If we want to use all
1107	three groups for a total of 2+2+4 = 8 pins (for an 8-bit MMC bus as is the
1108	case), we define a mapping like this:
1109	
1110	...
1111	{
1112		.dev_name = "foo-mmc.0",
1113		.name = "2bit"
1114		.type = PIN_MAP_TYPE_MUX_GROUP,
1115		.ctrl_dev_name = "pinctrl-foo",
1116		.function = "mmc0",
1117		.group = "mmc0_1_grp",
1118	},
1119	{
1120		.dev_name = "foo-mmc.0",
1121		.name = "4bit"
1122		.type = PIN_MAP_TYPE_MUX_GROUP,
1123		.ctrl_dev_name = "pinctrl-foo",
1124		.function = "mmc0",
1125		.group = "mmc0_1_grp",
1126	},
1127	{
1128		.dev_name = "foo-mmc.0",
1129		.name = "4bit"
1130		.type = PIN_MAP_TYPE_MUX_GROUP,
1131		.ctrl_dev_name = "pinctrl-foo",
1132		.function = "mmc0",
1133		.group = "mmc0_2_grp",
1134	},
1135	{
1136		.dev_name = "foo-mmc.0",
1137		.name = "8bit"
1138		.type = PIN_MAP_TYPE_MUX_GROUP,
1139		.ctrl_dev_name = "pinctrl-foo",
1140		.function = "mmc0",
1141		.group = "mmc0_1_grp",
1142	},
1143	{
1144		.dev_name = "foo-mmc.0",
1145		.name = "8bit"
1146		.type = PIN_MAP_TYPE_MUX_GROUP,
1147		.ctrl_dev_name = "pinctrl-foo",
1148		.function = "mmc0",
1149		.group = "mmc0_2_grp",
1150	},
1151	{
1152		.dev_name = "foo-mmc.0",
1153		.name = "8bit"
1154		.type = PIN_MAP_TYPE_MUX_GROUP,
1155		.ctrl_dev_name = "pinctrl-foo",
1156		.function = "mmc0",
1157		.group = "mmc0_3_grp",
1158	},
1159	...
1160	
1161	The result of grabbing this mapping from the device with something like
1162	this (see next paragraph):
1163	
1164		p = devm_pinctrl_get(dev);
1165		s = pinctrl_lookup_state(p, "8bit");
1166		ret = pinctrl_select_state(p, s);
1167	
1168	or more simply:
1169	
1170		p = devm_pinctrl_get_select(dev, "8bit");
1171	
1172	Will be that you activate all the three bottom records in the mapping at
1173	once. Since they share the same name, pin controller device, function and
1174	device, and since we allow multiple groups to match to a single device, they
1175	all get selected, and they all get enabled and disable simultaneously by the
1176	pinmux core.
1177	
1178	
1179	Pin control requests from drivers
1180	=================================
1181	
1182	When a device driver is about to probe the device core will automatically
1183	attempt to issue pinctrl_get_select_default() on these devices.
1184	This way driver writers do not need to add any of the boilerplate code
1185	of the type found below. However when doing fine-grained state selection
1186	and not using the "default" state, you may have to do some device driver
1187	handling of the pinctrl handles and states.
1188	
1189	So if you just want to put the pins for a certain device into the default
1190	state and be done with it, there is nothing you need to do besides
1191	providing the proper mapping table. The device core will take care of
1192	the rest.
1193	
1194	Generally it is discouraged to let individual drivers get and enable pin
1195	control. So if possible, handle the pin control in platform code or some other
1196	place where you have access to all the affected struct device * pointers. In
1197	some cases where a driver needs to e.g. switch between different mux mappings
1198	at runtime this is not possible.
1199	
1200	A typical case is if a driver needs to switch bias of pins from normal
1201	operation and going to sleep, moving from the PINCTRL_STATE_DEFAULT to
1202	PINCTRL_STATE_SLEEP at runtime, re-biasing or even re-muxing pins to save
1203	current in sleep mode.
1204	
1205	A driver may request a certain control state to be activated, usually just the
1206	default state like this:
1207	
1208	#include <linux/pinctrl/consumer.h>
1209	
1210	struct foo_state {
1211	       struct pinctrl *p;
1212	       struct pinctrl_state *s;
1213	       ...
1214	};
1215	
1216	foo_probe()
1217	{
1218		/* Allocate a state holder named "foo" etc */
1219		struct foo_state *foo = ...;
1220	
1221		foo->p = devm_pinctrl_get(&device);
1222		if (IS_ERR(foo->p)) {
1223			/* FIXME: clean up "foo" here */
1224			return PTR_ERR(foo->p);
1225		}
1226	
1227		foo->s = pinctrl_lookup_state(foo->p, PINCTRL_STATE_DEFAULT);
1228		if (IS_ERR(foo->s)) {
1229			/* FIXME: clean up "foo" here */
1230			return PTR_ERR(s);
1231		}
1232	
1233		ret = pinctrl_select_state(foo->s);
1234		if (ret < 0) {
1235			/* FIXME: clean up "foo" here */
1236			return ret;
1237		}
1238	}
1239	
1240	This get/lookup/select/put sequence can just as well be handled by bus drivers
1241	if you don't want each and every driver to handle it and you know the
1242	arrangement on your bus.
1243	
1244	The semantics of the pinctrl APIs are:
1245	
1246	- pinctrl_get() is called in process context to obtain a handle to all pinctrl
1247	  information for a given client device. It will allocate a struct from the
1248	  kernel memory to hold the pinmux state. All mapping table parsing or similar
1249	  slow operations take place within this API.
1250	
1251	- devm_pinctrl_get() is a variant of pinctrl_get() that causes pinctrl_put()
1252	  to be called automatically on the retrieved pointer when the associated
1253	  device is removed. It is recommended to use this function over plain
1254	  pinctrl_get().
1255	
1256	- pinctrl_lookup_state() is called in process context to obtain a handle to a
1257	  specific state for a the client device. This operation may be slow too.
1258	
1259	- pinctrl_select_state() programs pin controller hardware according to the
1260	  definition of the state as given by the mapping table. In theory this is a
1261	  fast-path operation, since it only involved blasting some register settings
1262	  into hardware. However, note that some pin controllers may have their
1263	  registers on a slow/IRQ-based bus, so client devices should not assume they
1264	  can call pinctrl_select_state() from non-blocking contexts.
1265	
1266	- pinctrl_put() frees all information associated with a pinctrl handle.
1267	
1268	- devm_pinctrl_put() is a variant of pinctrl_put() that may be used to
1269	  explicitly destroy a pinctrl object returned by devm_pinctrl_get().
1270	  However, use of this function will be rare, due to the automatic cleanup
1271	  that will occur even without calling it.
1272	
1273	  pinctrl_get() must be paired with a plain pinctrl_put().
1274	  pinctrl_get() may not be paired with devm_pinctrl_put().
1275	  devm_pinctrl_get() can optionally be paired with devm_pinctrl_put().
1276	  devm_pinctrl_get() may not be paired with plain pinctrl_put().
1277	
1278	Usually the pin control core handled the get/put pair and call out to the
1279	device drivers bookkeeping operations, like checking available functions and
1280	the associated pins, whereas the enable/disable pass on to the pin controller
1281	driver which takes care of activating and/or deactivating the mux setting by
1282	quickly poking some registers.
1283	
1284	The pins are allocated for your device when you issue the devm_pinctrl_get()
1285	call, after this you should be able to see this in the debugfs listing of all
1286	pins.
1287	
1288	NOTE: the pinctrl system will return -EPROBE_DEFER if it cannot find the
1289	requested pinctrl handles, for example if the pinctrl driver has not yet
1290	registered. Thus make sure that the error path in your driver gracefully
1291	cleans up and is ready to retry the probing later in the startup process.
1292	
1293	
1294	Drivers needing both pin control and GPIOs
1295	==========================================
1296	
1297	Again, it is discouraged to let drivers lookup and select pin control states
1298	themselves, but again sometimes this is unavoidable.
1299	
1300	So say that your driver is fetching its resources like this:
1301	
1302	#include <linux/pinctrl/consumer.h>
1303	#include <linux/gpio.h>
1304	
1305	struct pinctrl *pinctrl;
1306	int gpio;
1307	
1308	pinctrl = devm_pinctrl_get_select_default(&dev);
1309	gpio = devm_gpio_request(&dev, 14, "foo");
1310	
1311	Here we first request a certain pin state and then request GPIO 14 to be
1312	used. If you're using the subsystems orthogonally like this, you should
1313	nominally always get your pinctrl handle and select the desired pinctrl
1314	state BEFORE requesting the GPIO. This is a semantic convention to avoid
1315	situations that can be electrically unpleasant, you will certainly want to
1316	mux in and bias pins in a certain way before the GPIO subsystems starts to
1317	deal with them.
1318	
1319	The above can be hidden: using the device core, the pinctrl core may be
1320	setting up the config and muxing for the pins right before the device is
1321	probing, nevertheless orthogonal to the GPIO subsystem.
1322	
1323	But there are also situations where it makes sense for the GPIO subsystem
1324	to communicate directly with the pinctrl subsystem, using the latter as a
1325	back-end. This is when the GPIO driver may call out to the functions
1326	described in the section "Pin control interaction with the GPIO subsystem"
1327	above. This only involves per-pin multiplexing, and will be completely
1328	hidden behind the gpio_*() function namespace. In this case, the driver
1329	need not interact with the pin control subsystem at all.
1330	
1331	If a pin control driver and a GPIO driver is dealing with the same pins
1332	and the use cases involve multiplexing, you MUST implement the pin controller
1333	as a back-end for the GPIO driver like this, unless your hardware design
1334	is such that the GPIO controller can override the pin controller's
1335	multiplexing state through hardware without the need to interact with the
1336	pin control system.
1337	
1338	
1339	System pin control hogging
1340	==========================
1341	
1342	Pin control map entries can be hogged by the core when the pin controller
1343	is registered. This means that the core will attempt to call pinctrl_get(),
1344	lookup_state() and select_state() on it immediately after the pin control
1345	device has been registered.
1346	
1347	This occurs for mapping table entries where the client device name is equal
1348	to the pin controller device name, and the state name is PINCTRL_STATE_DEFAULT.
1349	
1350	{
1351		.dev_name = "pinctrl-foo",
1352		.name = PINCTRL_STATE_DEFAULT,
1353		.type = PIN_MAP_TYPE_MUX_GROUP,
1354		.ctrl_dev_name = "pinctrl-foo",
1355		.function = "power_func",
1356	},
1357	
1358	Since it may be common to request the core to hog a few always-applicable
1359	mux settings on the primary pin controller, there is a convenience macro for
1360	this:
1361	
1362	PIN_MAP_MUX_GROUP_HOG_DEFAULT("pinctrl-foo", NULL /* group */, "power_func")
1363	
1364	This gives the exact same result as the above construction.
1365	
1366	
1367	Runtime pinmuxing
1368	=================
1369	
1370	It is possible to mux a certain function in and out at runtime, say to move
1371	an SPI port from one set of pins to another set of pins. Say for example for
1372	spi0 in the example above, we expose two different groups of pins for the same
1373	function, but with different named in the mapping as described under
1374	"Advanced mapping" above. So that for an SPI device, we have two states named
1375	"pos-A" and "pos-B".
1376	
1377	This snippet first muxes the function in the pins defined by group A, enables
1378	it, disables and releases it, and muxes it in on the pins defined by group B:
1379	
1380	#include <linux/pinctrl/consumer.h>
1381	
1382	struct pinctrl *p;
1383	struct pinctrl_state *s1, *s2;
1384	
1385	foo_probe()
1386	{
1387		/* Setup */
1388		p = devm_pinctrl_get(&device);
1389		if (IS_ERR(p))
1390			...
1391	
1392		s1 = pinctrl_lookup_state(foo->p, "pos-A");
1393		if (IS_ERR(s1))
1394			...
1395	
1396		s2 = pinctrl_lookup_state(foo->p, "pos-B");
1397		if (IS_ERR(s2))
1398			...
1399	}
1400	
1401	foo_switch()
1402	{
1403		/* Enable on position A */
1404		ret = pinctrl_select_state(s1);
1405		if (ret < 0)
1406		    ...
1407	
1408		...
1409	
1410		/* Enable on position B */
1411		ret = pinctrl_select_state(s2);
1412		if (ret < 0)
1413		    ...
1414	
1415		...
1416	}
1417	
1418	The above has to be done from process context. The reservation of the pins
1419	will be done when the state is activated, so in effect one specific pin
1420	can be used by different functions at different times on a running system.
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