pinctrl.txt 50.3 KB
Newer Older
1 2 3 4 5 6 7 8 9
PINCTRL (PIN CONTROL) subsystem
This document outlines the pin control subsystem in Linux

This subsystem deals with:

- Enumerating and naming controllable pins

- Multiplexing of pins, pads, fingers (etc) see below for details

10 11 12
- Configuration of pins, pads, fingers (etc), such as software-controlled
  biasing and driving mode specific pins, such as pull-up/down, open drain,
  load capacitance etc.
13 14 15 16 17 18 19 20

Top-level interface
===================

Definition of PIN CONTROLLER:

- A pin controller is a piece of hardware, usually a set of registers, that
  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 24 25 26 27 28 29 30 31

Definition of PIN:

- PINS are equal to pads, fingers, balls or whatever packaging input or
  output line you want to control and these are denoted by unsigned integers
  in the range 0..maxpin. This numberspace is local to each PIN CONTROLLER, so
  there may be several such number spaces in a system. This pin space may
  be sparse - i.e. there may be gaps in the space with numbers where no
  pin exists.

32
When a PIN CONTROLLER is instantiated, it will register a descriptor to the
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
pin control framework, and this descriptor contains an array of pin descriptors
describing the pins handled by this specific pin controller.

Here is an example of a PGA (Pin Grid Array) chip seen from underneath:

        A   B   C   D   E   F   G   H

   8    o   o   o   o   o   o   o   o

   7    o   o   o   o   o   o   o   o

   6    o   o   o   o   o   o   o   o

   5    o   o   o   o   o   o   o   o

   4    o   o   o   o   o   o   o   o

   3    o   o   o   o   o   o   o   o

   2    o   o   o   o   o   o   o   o

   1    o   o   o   o   o   o   o   o

To register a pin controller and name all the pins on this package we can do
this in our driver:

#include <linux/pinctrl/pinctrl.h>

61 62 63 64
const struct pinctrl_pin_desc foo_pins[] = {
      PINCTRL_PIN(0, "A8"),
      PINCTRL_PIN(1, "B8"),
      PINCTRL_PIN(2, "C8"),
65
      ...
66 67 68
      PINCTRL_PIN(61, "F1"),
      PINCTRL_PIN(62, "G1"),
      PINCTRL_PIN(63, "H1"),
69 70 71 72 73 74 75 76 77 78 79 80 81
};

static struct pinctrl_desc foo_desc = {
	.name = "foo",
	.pins = foo_pins,
	.npins = ARRAY_SIZE(foo_pins),
	.owner = THIS_MODULE,
};

int __init foo_probe(void)
{
	struct pinctrl_dev *pctl;

82
	return pinctrl_register_and_init(&foo_desc, <PARENT>, NULL, &pctl);
83 84
}

85 86 87 88 89
To enable the pinctrl subsystem and the subgroups for PINMUX and PINCONF and
selected drivers, you need to select them from your machine's Kconfig entry,
since these are so tightly integrated with the machines they are used on.
See for example arch/arm/mach-u300/Kconfig for an example.

90
Pins usually have fancier names than this. You can find these in the datasheet
91 92
for your chip. Notice that the core pinctrl.h file provides a fancy macro
called PINCTRL_PIN() to create the struct entries. As you can see I enumerated
93 94
the pins from 0 in the upper left corner to 63 in the lower right corner.
This enumeration was arbitrarily chosen, in practice you need to think
95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134
through your numbering system so that it matches the layout of registers
and such things in your driver, or the code may become complicated. You must
also consider matching of offsets to the GPIO ranges that may be handled by
the pin controller.

For a padring with 467 pads, as opposed to actual pins, I used an enumeration
like this, walking around the edge of the chip, which seems to be industry
standard too (all these pads had names, too):


     0 ..... 104
   466        105
     .        .
     .        .
   358        224
    357 .... 225


Pin groups
==========

Many controllers need to deal with groups of pins, so the pin controller
subsystem has a mechanism for enumerating groups of pins and retrieving the
actual enumerated pins that are part of a certain group.

For example, say that we have a group of pins dealing with an SPI interface
on { 0, 8, 16, 24 }, and a group of pins dealing with an I2C interface on pins
on { 24, 25 }.

These two groups are presented to the pin control subsystem by implementing
some generic pinctrl_ops like this:

#include <linux/pinctrl/pinctrl.h>

struct foo_group {
	const char *name;
	const unsigned int *pins;
	const unsigned num_pins;
};

135 136
static const unsigned int spi0_pins[] = { 0, 8, 16, 24 };
static const unsigned int i2c0_pins[] = { 24, 25 };
137 138 139 140 141 142 143 144 145 146 147 148 149 150 151

static const struct foo_group foo_groups[] = {
	{
		.name = "spi0_grp",
		.pins = spi0_pins,
		.num_pins = ARRAY_SIZE(spi0_pins),
	},
	{
		.name = "i2c0_grp",
		.pins = i2c0_pins,
		.num_pins = ARRAY_SIZE(i2c0_pins),
	},
};


152
static int foo_get_groups_count(struct pinctrl_dev *pctldev)
153
{
154
	return ARRAY_SIZE(foo_groups);
155 156 157 158 159 160 161 162 163
}

static const char *foo_get_group_name(struct pinctrl_dev *pctldev,
				       unsigned selector)
{
	return foo_groups[selector].name;
}

static int foo_get_group_pins(struct pinctrl_dev *pctldev, unsigned selector,
164 165
			       const unsigned **pins,
			       unsigned *num_pins)
166 167 168 169 170 171 172
{
	*pins = (unsigned *) foo_groups[selector].pins;
	*num_pins = foo_groups[selector].num_pins;
	return 0;
}

static struct pinctrl_ops foo_pctrl_ops = {
173
	.get_groups_count = foo_get_groups_count,
174 175 176 177 178 179 180 181 182 183
	.get_group_name = foo_get_group_name,
	.get_group_pins = foo_get_group_pins,
};


static struct pinctrl_desc foo_desc = {
       ...
       .pctlops = &foo_pctrl_ops,
};

184
The pin control subsystem will call the .get_groups_count() function to
185
determine the total number of legal selectors, then it will call the other functions
186 187 188 189
to retrieve the name and pins of the group. Maintaining the data structure of
the groups is up to the driver, this is just a simple example - in practice you
may need more entries in your group structure, for example specific register
ranges associated with each group and so on.
190 191


192 193 194
Pin configuration
=================

195
Pins can sometimes be software-configured in various ways, mostly related
196 197 198 199 200 201 202
to their electronic properties when used as inputs or outputs. For example you
may be able to make an output pin high impedance, or "tristate" meaning it is
effectively disconnected. You may be able to connect an input pin to VDD or GND
using a certain resistor value - pull up and pull down - so that the pin has a
stable value when nothing is driving the rail it is connected to, or when it's
unconnected.

203 204
Pin configuration can be programmed by adding configuration entries into the
mapping table; see section "Board/machine configuration" below.
205

206 207 208 209 210
The format and meaning of the configuration parameter, PLATFORM_X_PULL_UP
above, is entirely defined by the pin controller driver.

The pin configuration driver implements callbacks for changing pin
configuration in the pin controller ops like this:
211 212 213 214 215

#include <linux/pinctrl/pinctrl.h>
#include <linux/pinctrl/pinconf.h>
#include "platform_x_pindefs.h"

Dong Aisheng's avatar
Dong Aisheng committed
216
static int foo_pin_config_get(struct pinctrl_dev *pctldev,
217 218 219 220 221 222 223 224 225 226
		    unsigned offset,
		    unsigned long *config)
{
	struct my_conftype conf;

	... Find setting for pin @ offset ...

	*config = (unsigned long) conf;
}

Dong Aisheng's avatar
Dong Aisheng committed
227
static int foo_pin_config_set(struct pinctrl_dev *pctldev,
228 229 230 231 232 233 234 235 236 237 238 239
		    unsigned offset,
		    unsigned long config)
{
	struct my_conftype *conf = (struct my_conftype *) config;

	switch (conf) {
		case PLATFORM_X_PULL_UP:
		...
		}
	}
}

Dong Aisheng's avatar
Dong Aisheng committed
240
static int foo_pin_config_group_get (struct pinctrl_dev *pctldev,
241 242 243 244 245 246
		    unsigned selector,
		    unsigned long *config)
{
	...
}

Dong Aisheng's avatar
Dong Aisheng committed
247
static int foo_pin_config_group_set (struct pinctrl_dev *pctldev,
248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275
		    unsigned selector,
		    unsigned long config)
{
	...
}

static struct pinconf_ops foo_pconf_ops = {
	.pin_config_get = foo_pin_config_get,
	.pin_config_set = foo_pin_config_set,
	.pin_config_group_get = foo_pin_config_group_get,
	.pin_config_group_set = foo_pin_config_group_set,
};

/* Pin config operations are handled by some pin controller */
static struct pinctrl_desc foo_desc = {
	...
	.confops = &foo_pconf_ops,
};

Since some controllers have special logic for handling entire groups of pins
they can exploit the special whole-group pin control function. The
pin_config_group_set() callback is allowed to return the error code -EAGAIN,
for groups it does not want to handle, or if it just wants to do some
group-level handling and then fall through to iterate over all pins, in which
case each individual pin will be treated by separate pin_config_set() calls as
well.


276 277 278 279 280 281
Interaction with the GPIO subsystem
===================================

The GPIO drivers may want to perform operations of various types on the same
physical pins that are also registered as pin controller pins.

282 283 284 285 286
First and foremost, the two subsystems can be used as completely orthogonal,
see the section named "pin control requests from drivers" and
"drivers needing both pin control and GPIOs" below for details. But in some
situations a cross-subsystem mapping between pins and GPIOs is needed.

287 288 289 290 291 292 293
Since the pin controller subsystem has its pinspace local to the pin controller
we need a mapping so that the pin control subsystem can figure out which pin
controller handles control of a certain GPIO pin. Since a single pin controller
may be muxing several GPIO ranges (typically SoCs that have one set of pins,
but internally several GPIO silicon blocks, each modelled as a struct
gpio_chip) any number of GPIO ranges can be added to a pin controller instance
like this:
294 295 296 297 298 299 300 301

struct gpio_chip chip_a;
struct gpio_chip chip_b;

static struct pinctrl_gpio_range gpio_range_a = {
	.name = "chip a",
	.id = 0,
	.base = 32,
302
	.pin_base = 32,
303 304 305 306
	.npins = 16,
	.gc = &chip_a;
};

307
static struct pinctrl_gpio_range gpio_range_b = {
308 309 310
	.name = "chip b",
	.id = 0,
	.base = 48,
311
	.pin_base = 64,
312 313 314 315 316 317 318 319 320 321 322 323
	.npins = 8,
	.gc = &chip_b;
};

{
	struct pinctrl_dev *pctl;
	...
	pinctrl_add_gpio_range(pctl, &gpio_range_a);
	pinctrl_add_gpio_range(pctl, &gpio_range_b);
}

So this complex system has one pin controller handling two different
324 325 326 327 328 329 330 331
GPIO chips. "chip a" has 16 pins and "chip b" has 8 pins. The "chip a" and
"chip b" have different .pin_base, which means a start pin number of the
GPIO range.

The GPIO range of "chip a" starts from the GPIO base of 32 and actual
pin range also starts from 32. However "chip b" has different starting
offset for the GPIO range and pin range. The GPIO range of "chip b" starts
from GPIO number 48, while the pin range of "chip b" starts from 64.
332

333 334 335 336 337 338 339 340 341
We can convert a gpio number to actual pin number using this "pin_base".
They are mapped in the global GPIO pin space at:

chip a:
 - GPIO range : [32 .. 47]
 - pin range  : [32 .. 47]
chip b:
 - GPIO range : [48 .. 55]
 - pin range  : [64 .. 71]
342

343 344 345 346 347 348 349 350 351 352 353 354 355 356 357
The above examples assume the mapping between the GPIOs and pins is
linear. If the mapping is sparse or haphazard, an array of arbitrary pin
numbers can be encoded in the range like this:

static const unsigned range_pins[] = { 14, 1, 22, 17, 10, 8, 6, 2 };

static struct pinctrl_gpio_range gpio_range = {
	.name = "chip",
	.id = 0,
	.base = 32,
	.pins = &range_pins,
	.npins = ARRAY_SIZE(range_pins),
	.gc = &chip;
};

358 359 360 361 362 363
In this case the pin_base property will be ignored. If the name of a pin
group is known, the pins and npins elements of the above structure can be
initialised using the function pinctrl_get_group_pins(), e.g. for pin
group "foo":

pinctrl_get_group_pins(pctl, "foo", &gpio_range.pins, &gpio_range.npins);
364

365
When GPIO-specific functions in the pin control subsystem are called, these
366
ranges will be used to look up the appropriate pin controller by inspecting
367 368 369 370 371
and matching the pin to the pin ranges across all controllers. When a
pin controller handling the matching range is found, GPIO-specific functions
will be called on that specific pin controller.

For all functionalities dealing with pin biasing, pin muxing etc, the pin
372
controller subsystem will look up the corresponding pin number from the passed
373
in gpio number, and use the range's internals to retrieve a pin number. After
374
that, the subsystem passes it on to the pin control driver, so the driver
375
will get a pin number into its handled number range. Further it is also passed
376 377 378
the range ID value, so that the pin controller knows which range it should
deal with.

379 380 381
Calling pinctrl_add_gpio_range from pinctrl driver is DEPRECATED. Please see
section 2.1 of Documentation/devicetree/bindings/gpio/gpio.txt on how to bind
pinctrl and gpio drivers.
382

383

384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429
PINMUX interfaces
=================

These calls use the pinmux_* naming prefix.  No other calls should use that
prefix.


What is pinmuxing?
==================

PINMUX, also known as padmux, ballmux, alternate functions or mission modes
is a way for chip vendors producing some kind of electrical packages to use
a certain physical pin (ball, pad, finger, etc) for multiple mutually exclusive
functions, depending on the application. By "application" in this context
we usually mean a way of soldering or wiring the package into an electronic
system, even though the framework makes it possible to also change the function
at runtime.

Here is an example of a PGA (Pin Grid Array) chip seen from underneath:

        A   B   C   D   E   F   G   H
      +---+
   8  | o | o   o   o   o   o   o   o
      |   |
   7  | o | o   o   o   o   o   o   o
      |   |
   6  | o | o   o   o   o   o   o   o
      +---+---+
   5  | o | o | o   o   o   o   o   o
      +---+---+               +---+
   4    o   o   o   o   o   o | o | o
                              |   |
   3    o   o   o   o   o   o | o | o
                              |   |
   2    o   o   o   o   o   o | o | o
      +-------+-------+-------+---+---+
   1  | o   o | o   o | o   o | o | o |
      +-------+-------+-------+---+---+

This is not tetris. The game to think of is chess. Not all PGA/BGA packages
are chessboard-like, big ones have "holes" in some arrangement according to
different design patterns, but we're using this as a simple example. Of the
pins you see some will be taken by things like a few VCC and GND to feed power
to the chip, and quite a few will be taken by large ports like an external
memory interface. The remaining pins will often be subject to pin multiplexing.

430 431
The example 8x8 PGA package above will have pin numbers 0 through 63 assigned
to its physical pins. It will name the pins { A1, A2, A3 ... H6, H7, H8 } using
432 433 434 435 436 437 438 439 440 441
pinctrl_register_pins() and a suitable data set as shown earlier.

In this 8x8 BGA package the pins { A8, A7, A6, A5 } can be used as an SPI port
(these are four pins: CLK, RXD, TXD, FRM). In that case, pin B5 can be used as
some general-purpose GPIO pin. However, in another setting, pins { A5, B5 } can
be used as an I2C port (these are just two pins: SCL, SDA). Needless to say,
we cannot use the SPI port and I2C port at the same time. However in the inside
of the package the silicon performing the SPI logic can alternatively be routed
out on pins { G4, G3, G2, G1 }.

442
On the bottom row at { A1, B1, C1, D1, E1, F1, G1, H1 } we have something
443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493
special - it's an external MMC bus that can be 2, 4 or 8 bits wide, and it will
consume 2, 4 or 8 pins respectively, so either { A1, B1 } are taken or
{ A1, B1, C1, D1 } or all of them. If we use all 8 bits, we cannot use the SPI
port on pins { G4, G3, G2, G1 } of course.

This way the silicon blocks present inside the chip can be multiplexed "muxed"
out on different pin ranges. Often contemporary SoC (systems on chip) will
contain several I2C, SPI, SDIO/MMC, etc silicon blocks that can be routed to
different pins by pinmux settings.

Since general-purpose I/O pins (GPIO) are typically always in shortage, it is
common to be able to use almost any pin as a GPIO pin if it is not currently
in use by some other I/O port.


Pinmux conventions
==================

The purpose of the pinmux functionality in the pin controller subsystem is to
abstract and provide pinmux settings to the devices you choose to instantiate
in your machine configuration. It is inspired by the clk, GPIO and regulator
subsystems, so devices will request their mux setting, but it's also possible
to request a single pin for e.g. GPIO.

Definitions:

- FUNCTIONS can be switched in and out by a driver residing with the pin
  control subsystem in the drivers/pinctrl/* directory of the kernel. The
  pin control driver knows the possible functions. In the example above you can
  identify three pinmux functions, one for spi, one for i2c and one for mmc.

- FUNCTIONS are assumed to be enumerable from zero in a one-dimensional array.
  In this case the array could be something like: { spi0, i2c0, mmc0 }
  for the three available functions.

- FUNCTIONS have PIN GROUPS as defined on the generic level - so a certain
  function is *always* associated with a certain set of pin groups, could
  be just a single one, but could also be many. In the example above the
  function i2c is associated with the pins { A5, B5 }, enumerated as
  { 24, 25 } in the controller pin space.

  The Function spi is associated with pin groups { A8, A7, A6, A5 }
  and { G4, G3, G2, G1 }, which are enumerated as { 0, 8, 16, 24 } and
  { 38, 46, 54, 62 } respectively.

  Group names must be unique per pin controller, no two groups on the same
  controller may have the same name.

- The combination of a FUNCTION and a PIN GROUP determine a certain function
  for a certain set of pins. The knowledge of the functions and pin groups
  and their machine-specific particulars are kept inside the pinmux driver,
494 495
  from the outside only the enumerators are known, and the driver core can
  request:
496

497
  - The name of a function with a certain selector (>= 0)
498
  - A list of groups associated with a certain function
499
  - That a certain group in that list to be activated for a certain function
500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522

  As already described above, pin groups are in turn self-descriptive, so
  the core will retrieve the actual pin range in a certain group from the
  driver.

- FUNCTIONS and GROUPS on a certain PIN CONTROLLER are MAPPED to a certain
  device by the board file, device tree or similar machine setup configuration
  mechanism, similar to how regulators are connected to devices, usually by
  name. Defining a pin controller, function and group thus uniquely identify
  the set of pins to be used by a certain device. (If only one possible group
  of pins is available for the function, no group name need to be supplied -
  the core will simply select the first and only group available.)

  In the example case we can define that this particular machine shall
  use device spi0 with pinmux function fspi0 group gspi0 and i2c0 on function
  fi2c0 group gi2c0, on the primary pin controller, we get mappings
  like these:

  {
    {"map-spi0", spi0, pinctrl0, fspi0, gspi0},
    {"map-i2c0", i2c0, pinctrl0, fi2c0, gi2c0}
  }

523 524 525 526
  Every map must be assigned a state name, pin controller, device and
  function. The group is not compulsory - if it is omitted the first group
  presented by the driver as applicable for the function will be selected,
  which is useful for simple cases.
527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546

  It is possible to map several groups to the same combination of device,
  pin controller and function. This is for cases where a certain function on
  a certain pin controller may use different sets of pins in different
  configurations.

- PINS for a certain FUNCTION using a certain PIN GROUP on a certain
  PIN CONTROLLER are provided on a first-come first-serve basis, so if some
  other device mux setting or GPIO pin request has already taken your physical
  pin, you will be denied the use of it. To get (activate) a new setting, the
  old one has to be put (deactivated) first.

Sometimes the documentation and hardware registers will be oriented around
pads (or "fingers") rather than pins - these are the soldering surfaces on the
silicon inside the package, and may or may not match the actual number of
pins/balls underneath the capsule. Pick some enumeration that makes sense to
you. Define enumerators only for the pins you can control if that makes sense.

Assumptions:

547
We assume that the number of possible function maps to pin groups is limited by
548
the hardware. I.e. we assume that there is no system where any function can be
549
mapped to any pin, like in a phone exchange. So the available pin groups for
550 551 552 553 554 555 556 557 558 559 560 561 562 563
a certain function will be limited to a few choices (say up to eight or so),
not hundreds or any amount of choices. This is the characteristic we have found
by inspecting available pinmux hardware, and a necessary assumption since we
expect pinmux drivers to present *all* possible function vs pin group mappings
to the subsystem.


Pinmux drivers
==============

The pinmux core takes care of preventing conflicts on pins and calling
the pin controller driver to execute different settings.

It is the responsibility of the pinmux driver to impose further restrictions
564
(say for example infer electronic limitations due to load, etc.) to determine
565 566 567 568 569
whether or not the requested function can actually be allowed, and in case it
is possible to perform the requested mux setting, poke the hardware so that
this happens.

Pinmux drivers are required to supply a few callback functions, some are
570 571
optional. Usually the set_mux() function is implemented, writing values into
some certain registers to activate a certain mux setting for a certain pin.
572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626

A simple driver for the above example will work by setting bits 0, 1, 2, 3 or 4
into some register named MUX to select a certain function with a certain
group of pins would work something like this:

#include <linux/pinctrl/pinctrl.h>
#include <linux/pinctrl/pinmux.h>

struct foo_group {
	const char *name;
	const unsigned int *pins;
	const unsigned num_pins;
};

static const unsigned spi0_0_pins[] = { 0, 8, 16, 24 };
static const unsigned spi0_1_pins[] = { 38, 46, 54, 62 };
static const unsigned i2c0_pins[] = { 24, 25 };
static const unsigned mmc0_1_pins[] = { 56, 57 };
static const unsigned mmc0_2_pins[] = { 58, 59 };
static const unsigned mmc0_3_pins[] = { 60, 61, 62, 63 };

static const struct foo_group foo_groups[] = {
	{
		.name = "spi0_0_grp",
		.pins = spi0_0_pins,
		.num_pins = ARRAY_SIZE(spi0_0_pins),
	},
	{
		.name = "spi0_1_grp",
		.pins = spi0_1_pins,
		.num_pins = ARRAY_SIZE(spi0_1_pins),
	},
	{
		.name = "i2c0_grp",
		.pins = i2c0_pins,
		.num_pins = ARRAY_SIZE(i2c0_pins),
	},
	{
		.name = "mmc0_1_grp",
		.pins = mmc0_1_pins,
		.num_pins = ARRAY_SIZE(mmc0_1_pins),
	},
	{
		.name = "mmc0_2_grp",
		.pins = mmc0_2_pins,
		.num_pins = ARRAY_SIZE(mmc0_2_pins),
	},
	{
		.name = "mmc0_3_grp",
		.pins = mmc0_3_pins,
		.num_pins = ARRAY_SIZE(mmc0_3_pins),
	},
};


627
static int foo_get_groups_count(struct pinctrl_dev *pctldev)
628
{
629
	return ARRAY_SIZE(foo_groups);
630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647
}

static const char *foo_get_group_name(struct pinctrl_dev *pctldev,
				       unsigned selector)
{
	return foo_groups[selector].name;
}

static int foo_get_group_pins(struct pinctrl_dev *pctldev, unsigned selector,
			       unsigned ** const pins,
			       unsigned * const num_pins)
{
	*pins = (unsigned *) foo_groups[selector].pins;
	*num_pins = foo_groups[selector].num_pins;
	return 0;
}

static struct pinctrl_ops foo_pctrl_ops = {
648
	.get_groups_count = foo_get_groups_count,
649 650 651 652 653 654 655 656 657 658
	.get_group_name = foo_get_group_name,
	.get_group_pins = foo_get_group_pins,
};

struct foo_pmx_func {
	const char *name;
	const char * const *groups;
	const unsigned num_groups;
};

659
static const char * const spi0_groups[] = { "spi0_0_grp", "spi0_1_grp" };
660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681
static const char * const i2c0_groups[] = { "i2c0_grp" };
static const char * const mmc0_groups[] = { "mmc0_1_grp", "mmc0_2_grp",
					"mmc0_3_grp" };

static const struct foo_pmx_func foo_functions[] = {
	{
		.name = "spi0",
		.groups = spi0_groups,
		.num_groups = ARRAY_SIZE(spi0_groups),
	},
	{
		.name = "i2c0",
		.groups = i2c0_groups,
		.num_groups = ARRAY_SIZE(i2c0_groups),
	},
	{
		.name = "mmc0",
		.groups = mmc0_groups,
		.num_groups = ARRAY_SIZE(mmc0_groups),
	},
};

682
static int foo_get_functions_count(struct pinctrl_dev *pctldev)
683
{
684
	return ARRAY_SIZE(foo_functions);
685 686
}

687
static const char *foo_get_fname(struct pinctrl_dev *pctldev, unsigned selector)
688
{
689
	return foo_functions[selector].name;
690 691 692 693 694 695 696 697 698 699 700
}

static int foo_get_groups(struct pinctrl_dev *pctldev, unsigned selector,
			  const char * const **groups,
			  unsigned * const num_groups)
{
	*groups = foo_functions[selector].groups;
	*num_groups = foo_functions[selector].num_groups;
	return 0;
}

701
static int foo_set_mux(struct pinctrl_dev *pctldev, unsigned selector,
702 703
		unsigned group)
{
704
	u8 regbit = (1 << selector + group);
705 706 707 708 709

	writeb((readb(MUX)|regbit), MUX)
	return 0;
}

710
static struct pinmux_ops foo_pmxops = {
711
	.get_functions_count = foo_get_functions_count,
712 713
	.get_function_name = foo_get_fname,
	.get_function_groups = foo_get_groups,
714
	.set_mux = foo_set_mux,
715
	.strict = true,
716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738
};

/* Pinmux operations are handled by some pin controller */
static struct pinctrl_desc foo_desc = {
	...
	.pctlops = &foo_pctrl_ops,
	.pmxops = &foo_pmxops,
};

In the example activating muxing 0 and 1 at the same time setting bits
0 and 1, uses one pin in common so they would collide.

The beauty of the pinmux subsystem is that since it keeps track of all
pins and who is using them, it will already have denied an impossible
request like that, so the driver does not need to worry about such
things - when it gets a selector passed in, the pinmux subsystem makes
sure no other device or GPIO assignment is already using the selected
pins. Thus bits 0 and 1 in the control register will never be set at the
same time.

All the above functions are mandatory to implement for a pinmux driver.


739 740
Pin control interaction with the GPIO subsystem
===============================================
741

742 743 744
Note that the following implies that the use case is to use a certain pin
from the Linux kernel using the API in <linux/gpio.h> with gpio_request()
and similar functions. There are cases where you may be using something
745
that your datasheet calls "GPIO mode", but actually is just an electrical
746 747 748
configuration for a certain device. See the section below named
"GPIO mode pitfalls" for more details on this scenario.

749 750
The public pinmux API contains two functions named pinctrl_request_gpio()
and pinctrl_free_gpio(). These two functions shall *ONLY* be called from
751
gpiolib-based drivers as part of their gpio_request() and
752
gpio_free() semantics. Likewise the pinctrl_gpio_direction_[input|output]
753 754 755 756
shall only be called from within respective gpio_direction_[input|output]
gpiolib implementation.

NOTE that platforms and individual drivers shall *NOT* request GPIO pins to be
757 758
controlled e.g. muxed in. Instead, implement a proper gpiolib driver and have
that driver request proper muxing and other control for its pins.
759

760 761 762 763 764 765 766
The function list could become long, especially if you can convert every
individual pin into a GPIO pin independent of any other pins, and then try
the approach to define every pin as a function.

In this case, the function array would become 64 entries for each GPIO
setting and then the device functions.

767
For this reason there are two functions a pin control driver can implement
768 769
to enable only GPIO on an individual pin: .gpio_request_enable() and
.gpio_disable_free().
770 771 772 773 774

This function will pass in the affected GPIO range identified by the pin
controller core, so you know which GPIO pins are being affected by the request
operation.

775 776 777 778 779 780 781
If your driver needs to have an indication from the framework of whether the
GPIO pin shall be used for input or output you can implement the
.gpio_set_direction() function. As described this shall be called from the
gpiolib driver and the affected GPIO range, pin offset and desired direction
will be passed along to this function.

Alternatively to using these special functions, it is fully allowed to use
782
named functions for each GPIO pin, the pinctrl_request_gpio() will attempt to
783 784
obtain the function "gpioN" where "N" is the global GPIO pin number if no
special GPIO-handler is registered.
785 786


787 788 789
GPIO mode pitfalls
==================

790 791 792 793 794 795 796 797
Due to the naming conventions used by hardware engineers, where "GPIO"
is taken to mean different things than what the kernel does, the developer
may be confused by a datasheet talking about a pin being possible to set
into "GPIO mode". It appears that what hardware engineers mean with
"GPIO mode" is not necessarily the use case that is implied in the kernel
interface <linux/gpio.h>: a pin that you grab from kernel code and then
either listen for input or drive high/low to assert/deassert some
external line.
798 799 800 801 802 803

Rather hardware engineers think that "GPIO mode" means that you can
software-control a few electrical properties of the pin that you would
not be able to control if the pin was in some other mode, such as muxed in
for a device.

804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831
The GPIO portions of a pin and its relation to a certain pin controller
configuration and muxing logic can be constructed in several ways. Here
are two examples:

(A)
                       pin config
                       logic regs
                       |               +- SPI
     Physical pins --- pad --- pinmux -+- I2C
                               |       +- mmc
                               |       +- GPIO
                               pin
                               multiplex
                               logic regs

Here some electrical properties of the pin can be configured no matter
whether the pin is used for GPIO or not. If you multiplex a GPIO onto a
pin, you can also drive it high/low from "GPIO" registers.
Alternatively, the pin can be controlled by a certain peripheral, while
still applying desired pin config properties. GPIO functionality is thus
orthogonal to any other device using the pin.

In this arrangement the registers for the GPIO portions of the pin controller,
or the registers for the GPIO hardware module are likely to reside in a
separate memory range only intended for GPIO driving, and the register
range dealing with pin config and pin multiplexing get placed into a
different memory range and a separate section of the data sheet.

832
A flag "strict" in struct pinmux_ops is available to check and deny
833 834 835 836
simultaneous access to the same pin from GPIO and pin multiplexing
consumers on hardware of this type. The pinctrl driver should set this flag
accordingly.

837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856
(B)

                       pin config
                       logic regs
                       |               +- SPI
     Physical pins --- pad --- pinmux -+- I2C
                       |       |       +- mmc
                       |       |
                       GPIO    pin
                               multiplex
                               logic regs

In this arrangement, the GPIO functionality can always be enabled, such that
e.g. a GPIO input can be used to "spy" on the SPI/I2C/MMC signal while it is
pulsed out. It is likely possible to disrupt the traffic on the pin by doing
wrong things on the GPIO block, as it is never really disconnected. It is
possible that the GPIO, pin config and pin multiplex registers are placed into
the same memory range and the same section of the data sheet, although that
need not be the case.

857 858 859 860 861
In some pin controllers, although the physical pins are designed in the same
way as (B), the GPIO function still can't be enabled at the same time as the
peripheral functions. So again the "strict" flag should be set, denying
simultaneous activation by GPIO and other muxed in devices.

862 863 864 865 866 867 868 869 870
From a kernel point of view, however, these are different aspects of the
hardware and shall be put into different subsystems:

- Registers (or fields within registers) that control electrical
  properties of the pin such as biasing and drive strength should be
  exposed through the pinctrl subsystem, as "pin configuration" settings.

- Registers (or fields within registers) that control muxing of signals
  from various other HW blocks (e.g. I2C, MMC, or GPIO) onto pins should
871
  be exposed through the pinctrl subsystem, as mux functions.
872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890

- Registers (or fields within registers) that control GPIO functionality
  such as setting a GPIO's output value, reading a GPIO's input value, or
  setting GPIO pin direction should be exposed through the GPIO subsystem,
  and if they also support interrupt capabilities, through the irqchip
  abstraction.

Depending on the exact HW register design, some functions exposed by the
GPIO subsystem may call into the pinctrl subsystem in order to
co-ordinate register settings across HW modules. In particular, this may
be needed for HW with separate GPIO and pin controller HW modules, where
e.g. GPIO direction is determined by a register in the pin controller HW
module rather than the GPIO HW module.

Electrical properties of the pin such as biasing and drive strength
may be placed at some pin-specific register in all cases or as part
of the GPIO register in case (B) especially. This doesn't mean that such
properties necessarily pertain to what the Linux kernel calls "GPIO".

891 892 893 894
Example: a pin is usually muxed in to be used as a UART TX line. But during
system sleep, we need to put this pin into "GPIO mode" and ground it.

If you make a 1-to-1 map to the GPIO subsystem for this pin, you may start
895
to think that you need to come up with something really complex, that the
896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939
pin shall be used for UART TX and GPIO at the same time, that you will grab
a pin control handle and set it to a certain state to enable UART TX to be
muxed in, then twist it over to GPIO mode and use gpio_direction_output()
to drive it low during sleep, then mux it over to UART TX again when you
wake up and maybe even gpio_request/gpio_free as part of this cycle. This
all gets very complicated.

The solution is to not think that what the datasheet calls "GPIO mode"
has to be handled by the <linux/gpio.h> interface. Instead view this as
a certain pin config setting. Look in e.g. <linux/pinctrl/pinconf-generic.h>
and you find this in the documentation:

  PIN_CONFIG_OUTPUT: this will configure the pin in output, use argument
     1 to indicate high level, argument 0 to indicate low level.

So it is perfectly possible to push a pin into "GPIO mode" and drive the
line low as part of the usual pin control map. So for example your UART
driver may look like this:

#include <linux/pinctrl/consumer.h>

struct pinctrl          *pinctrl;
struct pinctrl_state    *pins_default;
struct pinctrl_state    *pins_sleep;

pins_default = pinctrl_lookup_state(uap->pinctrl, PINCTRL_STATE_DEFAULT);
pins_sleep = pinctrl_lookup_state(uap->pinctrl, PINCTRL_STATE_SLEEP);

/* Normal mode */
retval = pinctrl_select_state(pinctrl, pins_default);
/* Sleep mode */
retval = pinctrl_select_state(pinctrl, pins_sleep);

And your machine configuration may look like this:
--------------------------------------------------

static unsigned long uart_default_mode[] = {
    PIN_CONF_PACKED(PIN_CONFIG_DRIVE_PUSH_PULL, 0),
};

static unsigned long uart_sleep_mode[] = {
    PIN_CONF_PACKED(PIN_CONFIG_OUTPUT, 0),
};

940
static struct pinctrl_map pinmap[] __initdata = {
941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963
    PIN_MAP_MUX_GROUP("uart", PINCTRL_STATE_DEFAULT, "pinctrl-foo",
                      "u0_group", "u0"),
    PIN_MAP_CONFIGS_PIN("uart", PINCTRL_STATE_DEFAULT, "pinctrl-foo",
                        "UART_TX_PIN", uart_default_mode),
    PIN_MAP_MUX_GROUP("uart", PINCTRL_STATE_SLEEP, "pinctrl-foo",
                      "u0_group", "gpio-mode"),
    PIN_MAP_CONFIGS_PIN("uart", PINCTRL_STATE_SLEEP, "pinctrl-foo",
                        "UART_TX_PIN", uart_sleep_mode),
};

foo_init(void) {
    pinctrl_register_mappings(pinmap, ARRAY_SIZE(pinmap));
}

Here the pins we want to control are in the "u0_group" and there is some
function called "u0" that can be enabled on this group of pins, and then
everything is UART business as usual. But there is also some function
named "gpio-mode" that can be mapped onto the same pins to move them into
GPIO mode.

This will give the desired effect without any bogus interaction with the
GPIO subsystem. It is just an electrical configuration used by that device
when going to sleep, it might imply that the pin is set into something the
964
datasheet calls "GPIO mode", but that is not the point: it is still used
965 966 967 968
by that UART device to control the pins that pertain to that very UART
driver, putting them into modes needed by the UART. GPIO in the Linux
kernel sense are just some 1-bit line, and is a different use case.

969
How the registers are poked to attain the push or pull, and output low
970 971 972 973 974 975 976
configuration and the muxing of the "u0" or "gpio-mode" group onto these
pins is a question for the driver.

Some datasheets will be more helpful and refer to the "GPIO mode" as
"low power mode" rather than anything to do with GPIO. This often means
the same thing electrically speaking, but in this latter case the
software engineers will usually quickly identify that this is some
977
specific muxing or configuration rather than anything related to the GPIO
978 979 980
API.


981
Board/machine configuration
982 983 984 985 986 987 988
==================================

Boards and machines define how a certain complete running system is put
together, including how GPIOs and devices are muxed, how regulators are
constrained and how the clock tree looks. Of course pinmux settings are also
part of this.

989 990 991
A pin controller configuration for a machine looks pretty much like a simple
regulator configuration, so for the example array above we want to enable i2c
and spi on the second function mapping:
992 993 994

#include <linux/pinctrl/machine.h>

995
static const struct pinctrl_map mapping[] __initconst = {
996
	{
997
		.dev_name = "foo-spi.0",
998
		.name = PINCTRL_STATE_DEFAULT,
999
		.type = PIN_MAP_TYPE_MUX_GROUP,
1000
		.ctrl_dev_name = "pinctrl-foo",
1001
		.data.mux.function = "spi0",
1002 1003
	},
	{
1004
		.dev_name = "foo-i2c.0",
1005
		.name = PINCTRL_STATE_DEFAULT,
1006
		.type = PIN_MAP_TYPE_MUX_GROUP,
1007
		.ctrl_dev_name = "pinctrl-foo",
1008
		.data.mux.function = "i2c0",
1009 1010
	},
	{
1011
		.dev_name = "foo-mmc.0",
1012
		.name = PINCTRL_STATE_DEFAULT,
1013
		.type = PIN_MAP_TYPE_MUX_GROUP,
1014
		.ctrl_dev_name = "pinctrl-foo",
1015
		.data.mux.function = "mmc0",
1016 1017 1018 1019 1020 1021 1022 1023
	},
};

The dev_name here matches to the unique device name that can be used to look
up the device struct (just like with clockdev or regulators). The function name
must match a function provided by the pinmux driver handling this pin range.

As you can see we may have several pin controllers on the system and thus
1024
we need to specify which one of them contains the functions we wish to map.
1025 1026 1027

You register this pinmux mapping to the pinmux subsystem by simply:

1028
       ret = pinctrl_register_mappings(mapping, ARRAY_SIZE(mapping));
1029 1030

Since the above construct is pretty common there is a helper macro to make
1031
it even more compact which assumes you want to use pinctrl-foo and position
1032 1033
0 for mapping, for example:

1034
static struct pinctrl_map mapping[] __initdata = {
1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052
	PIN_MAP_MUX_GROUP("foo-i2c.o", PINCTRL_STATE_DEFAULT, "pinctrl-foo", NULL, "i2c0"),
};

The mapping table may also contain pin configuration entries. It's common for
each pin/group to have a number of configuration entries that affect it, so
the table entries for configuration reference an array of config parameters
and values. An example using the convenience macros is shown below:

static unsigned long i2c_grp_configs[] = {
	FOO_PIN_DRIVEN,
	FOO_PIN_PULLUP,
};

static unsigned long i2c_pin_configs[] = {
	FOO_OPEN_COLLECTOR,
	FOO_SLEW_RATE_SLOW,
};

1053
static struct pinctrl_map mapping[] __initdata = {
1054
	PIN_MAP_MUX_GROUP("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0", "i2c0"),
1055 1056 1057
	PIN_MAP_CONFIGS_GROUP("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0", i2c_grp_configs),
	PIN_MAP_CONFIGS_PIN("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0scl", i2c_pin_configs),
	PIN_MAP_CONFIGS_PIN("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0sda", i2c_pin_configs),
1058 1059 1060 1061 1062 1063 1064 1065 1066
};

Finally, some devices expect the mapping table to contain certain specific
named states. When running on hardware that doesn't need any pin controller
configuration, the mapping table must still contain those named states, in
order to explicitly indicate that the states were provided and intended to
be empty. Table entry macro PIN_MAP_DUMMY_STATE serves the purpose of defining
a named state without causing any pin controller to be programmed:

1067
static struct pinctrl_map mapping[] __initdata = {
1068
	PIN_MAP_DUMMY_STATE("foo-i2c.0", PINCTRL_STATE_DEFAULT),
1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079
};


Complex mappings
================

As it is possible to map a function to different groups of pins an optional
.group can be specified like this:

...
{
1080
	.dev_name = "foo-spi.0",
1081
	.name = "spi0-pos-A",
1082
	.type = PIN_MAP_TYPE_MUX_GROUP,
1083
	.ctrl_dev_name = "pinctrl-foo",
1084 1085 1086 1087
	.function = "spi0",
	.group = "spi0_0_grp",
},
{
1088
	.dev_name = "foo-spi.0",
1089
	.name = "spi0-pos-B",
1090
	.type = PIN_MAP_TYPE_MUX_GROUP,
1091
	.ctrl_dev_name = "pinctrl-foo",
1092 1093 1094 1095 1096 1097 1098 1099
	.function = "spi0",
	.group = "spi0_1_grp",
},
...

This example mapping is used to switch between two positions for spi0 at
runtime, as described further below under the heading "Runtime pinmuxing".

1100 1101
Further it is possible for one named state to affect the muxing of several
groups of pins, say for example in the mmc0 example above, where you can
1102 1103 1104 1105 1106 1107
additively expand the mmc0 bus from 2 to 4 to 8 pins. If we want to use all
three groups for a total of 2+2+4 = 8 pins (for an 8-bit MMC bus as is the
case), we define a mapping like this:

...
{
1108
	.dev_name = "foo-mmc.0",
1109
	.name = "2bit"
1110
	.type = PIN_MAP_TYPE_MUX_GROUP,
1111
	.ctrl_dev_name = "pinctrl-foo",
1112
	.function = "mmc0",
1113
	.group = "mmc0_1_grp",
1114 1115
},
{
1116
	.dev_name = "foo-mmc.0",
1117
	.name = "4bit"
1118
	.type = PIN_MAP_TYPE_MUX_GROUP,
1119
	.ctrl_dev_name = "pinctrl-foo",
1120
	.function = "mmc0",
1121
	.group = "mmc0_1_grp",
1122 1123
},
{
1124
	.dev_name = "foo-mmc.0",
1125
	.name = "4bit"
1126
	.type = PIN_MAP_TYPE_MUX_GROUP,
1127
	.ctrl_dev_name = "pinctrl-foo",
1128
	.function = "mmc0",
1129
	.group = "mmc0_2_grp",
1130 1131
},
{
1132
	.dev_name = "foo-mmc.0",
1133
	.name = "8bit"
1134
	.type = PIN_MAP_TYPE_MUX_GROUP,
1135
	.ctrl_dev_name = "pinctrl-foo",
1136
	.function = "mmc0",
1137
	.group = "mmc0_1_grp",
1138 1139
},
{
1140
	.dev_name = "foo-mmc.0",
1141
	.name = "8bit"
1142
	.type = PIN_MAP_TYPE_MUX_GROUP,
1143
	.ctrl_dev_name = "pinctrl-foo",
1144
	.function = "mmc0",
1145
	.group = "mmc0_2_grp",
1146 1147
},
{
1148
	.dev_name = "foo-mmc.0",
1149
	.name = "8bit"
1150
	.type = PIN_MAP_TYPE_MUX_GROUP,
1151
	.ctrl_dev_name = "pinctrl-foo",
1152
	.function = "mmc0",
1153
	.group = "mmc0_3_grp",
1154 1155 1156 1157 1158 1159
},
...

The result of grabbing this mapping from the device with something like
this (see next paragraph):

1160
	p = devm_pinctrl_get(dev);
1161 1162 1163 1164 1165
	s = pinctrl_lookup_state(p, "8bit");
	ret = pinctrl_select_state(p, s);

or more simply:

1166
	p = devm_pinctrl_get_select(dev, "8bit");
1167 1168

Will be that you activate all the three bottom records in the mapping at
1169
once. Since they share the same name, pin controller device, function and
1170 1171 1172 1173 1174
device, and since we allow multiple groups to match to a single device, they
all get selected, and they all get enabled and disable simultaneously by the
pinmux core.


1175 1176
Pin control requests from drivers
=================================
1177

1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189
When a device driver is about to probe the device core will automatically
attempt to issue pinctrl_get_select_default() on these devices.
This way driver writers do not need to add any of the boilerplate code
of the type found below. However when doing fine-grained state selection
and not using the "default" state, you may have to do some device driver
handling of the pinctrl handles and states.

So if you just want to put the pins for a certain device into the default
state and be done with it, there is nothing you need to do besides
providing the proper mapping table. The device core will take care of
the rest.

1190 1191 1192 1193 1194
Generally it is discouraged to let individual drivers get and enable pin
control. So if possible, handle the pin control in platform code or some other
place where you have access to all the affected struct device * pointers. In
some cases where a driver needs to e.g. switch between different mux mappings
at runtime this is not possible.
1195

1196 1197 1198 1199 1200
A typical case is if a driver needs to switch bias of pins from normal
operation and going to sleep, moving from the PINCTRL_STATE_DEFAULT to
PINCTRL_STATE_SLEEP at runtime, re-biasing or even re-muxing pins to save
current in sleep mode.

1201 1202
A driver may request a certain control state to be activated, usually just the
default state like this:
1203

1204
#include <linux/pinctrl/consumer.h>
1205 1206

struct foo_state {
1207
       struct pinctrl *p;
1208
       struct pinctrl_state *s;
1209 1210 1211 1212 1213
       ...
};

foo_probe()
{
1214 1215 1216
	/* Allocate a state holder named "foo" etc */
	struct foo_state *foo = ...;

1217
	foo->p = devm_pinctrl_get(&device);
1218 1219 1220 1221
	if (IS_ERR(foo->p)) {
		/* FIXME: clean up "foo" here */
		return PTR_ERR(foo->p);
	}
1222

1223 1224 1225 1226 1227
	foo->s = pinctrl_lookup_state(foo->p, PINCTRL_STATE_DEFAULT);
	if (IS_ERR(foo->s)) {
		/* FIXME: clean up "foo" here */
		return PTR_ERR(s);
	}
1228

1229 1230 1231 1232 1233
	ret = pinctrl_select_state(foo->s);
	if (ret < 0) {
		/* FIXME: clean up "foo" here */
		return ret;
	}
1234 1235
}

1236
This get/lookup/select/put sequence can just as well be handled by bus drivers
1237 1238 1239
if you don't want each and every driver to handle it and you know the
arrangement on your bus.

1240 1241 1242 1243 1244 1245
The semantics of the pinctrl APIs are:

- pinctrl_get() is called in process context to obtain a handle to all pinctrl
  information for a given client device. It will allocate a struct from the
  kernel memory to hold the pinmux state. All mapping table parsing or similar
  slow operations take place within this API.
1246

1247 1248 1249 1250 1251
- devm_pinctrl_get() is a variant of pinctrl_get() that causes pinctrl_put()
  to be called automatically on the retrieved pointer when the associated
  device is removed. It is recommended to use this function over plain
  pinctrl_get().

1252
- pinctrl_lookup_state() is called in process context to obtain a handle to a
1253
  specific state for a client device. This operation may be slow, too.
1254

1255
- pinctrl_select_state() programs pin controller hardware according to the
1256
  definition of the state as given by the mapping table. In theory, this is a
1257 1258 1259 1260
  fast-path operation, since it only involved blasting some register settings
  into hardware. However, note that some pin controllers may have their
  registers on a slow/IRQ-based bus, so client devices should not assume they
  can call pinctrl_select_state() from non-blocking contexts.
1261

1262
- pinctrl_put() frees all information associated with a pinctrl handle.
1263

1264 1265 1266 1267 1268 1269 1270 1271 1272 1273
- devm_pinctrl_put() is a variant of pinctrl_put() that may be used to
  explicitly destroy a pinctrl object returned by devm_pinctrl_get().
  However, use of this function will be rare, due to the automatic cleanup
  that will occur even without calling it.

  pinctrl_get() must be paired with a plain pinctrl_put().
  pinctrl_get() may not be paired with devm_pinctrl_put().
  devm_pinctrl_get() can optionally be paired with devm_pinctrl_put().
  devm_pinctrl_get() may not be paired with plain pinctrl_put().

1274 1275
Usually the pin control core handled the get/put pair and call out to the
device drivers bookkeeping operations, like checking available functions and
1276
the associated pins, whereas select_state pass on to the pin controller
1277 1278 1279
driver which takes care of activating and/or deactivating the mux setting by
quickly poking some registers.

1280 1281 1282
The pins are allocated for your device when you issue the devm_pinctrl_get()
call, after this you should be able to see this in the debugfs listing of all
pins.
1283

1284 1285 1286 1287 1288
NOTE: the pinctrl system will return -EPROBE_DEFER if it cannot find the
requested pinctrl handles, for example if the pinctrl driver has not yet
registered. Thus make sure that the error path in your driver gracefully
cleans up and is ready to retry the probing later in the startup process.

1289

1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314
Drivers needing both pin control and GPIOs
==========================================

Again, it is discouraged to let drivers lookup and select pin control states
themselves, but again sometimes this is unavoidable.

So say that your driver is fetching its resources like this:

#include <linux/pinctrl/consumer.h>
#include <linux/gpio.h>

struct pinctrl *pinctrl;
int gpio;

pinctrl = devm_pinctrl_get_select_default(&dev);
gpio = devm_gpio_request(&dev, 14, "foo");

Here we first request a certain pin state and then request GPIO 14 to be
used. If you're using the subsystems orthogonally like this, you should
nominally always get your pinctrl handle and select the desired pinctrl
state BEFORE requesting the GPIO. This is a semantic convention to avoid
situations that can be electrically unpleasant, you will certainly want to
mux in and bias pins in a certain way before the GPIO subsystems starts to
deal with them.

1315 1316 1317
The above can be hidden: using the device core, the pinctrl core may be
setting up the config and muxing for the pins right before the device is
probing, nevertheless orthogonal to the GPIO subsystem.
1318 1319

But there are also situations where it makes sense for the GPIO subsystem
1320 1321
to communicate directly with the pinctrl subsystem, using the latter as a
back-end. This is when the GPIO driver may call out to the functions
1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334
described in the section "Pin control interaction with the GPIO subsystem"
above. This only involves per-pin multiplexing, and will be completely
hidden behind the gpio_*() function namespace. In this case, the driver
need not interact with the pin control subsystem at all.

If a pin control driver and a GPIO driver is dealing with the same pins
and the use cases involve multiplexing, you MUST implement the pin controller
as a back-end for the GPIO driver like this, unless your hardware design
is such that the GPIO controller can override the pin controller's
multiplexing state through hardware without the need to interact with the
pin control system.


1335 1336
System pin control hogging
==========================
1337

1338
Pin control map entries can be hogged by the core when the pin controller
1339 1340 1341
is registered. This means that the core will attempt to call pinctrl_get(),
lookup_state() and select_state() on it immediately after the pin control
device has been registered.
1342

1343 1344
This occurs for mapping table entries where the client device name is equal
to the pin controller device name, and the state name is PINCTRL_STATE_DEFAULT.
1345 1346

{
1347
	.dev_name = "pinctrl-foo",
1348
	.name = PINCTRL_STATE_DEFAULT,
1349
	.type = PIN_MAP_TYPE_MUX_GROUP,
1350
	.ctrl_dev_name = "pinctrl-foo",
1351 1352 1353 1354 1355 1356 1357
	.function = "power_func",
},

Since it may be common to request the core to hog a few always-applicable
mux settings on the primary pin controller, there is a convenience macro for
this:

1358
PIN_MAP_MUX_GROUP_HOG_DEFAULT("pinctrl-foo", NULL /* group */, "power_func")
1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369

This gives the exact same result as the above construction.


Runtime pinmuxing
=================

It is possible to mux a certain function in and out at runtime, say to move
an SPI port from one set of pins to another set of pins. Say for example for
spi0 in the example above, we expose two different groups of pins for the same
function, but with different named in the mapping as described under
1370 1371
"Advanced mapping" above. So that for an SPI device, we have two states named
"pos-A" and "pos-B".
1372

1373 1374 1375
This snippet first initializes a state object for both groups (in foo_probe()),
then muxes the function in the pins defined by group A, and finally muxes it in
on the pins defined by group B:
1376

1377 1378
#include <linux/pinctrl/consumer.h>

1379 1380
struct pinctrl *p;
struct pinctrl_state *s1, *s2;
1381

1382 1383
foo_probe()
{
1384
	/* Setup */
1385
	p = devm_pinctrl_get(&device);
1386 1387 1388 1389 1390 1391 1392 1393 1394 1395
	if (IS_ERR(p))
		...

	s1 = pinctrl_lookup_state(foo->p, "pos-A");
	if (IS_ERR(s1))
		...

	s2 = pinctrl_lookup_state(foo->p, "pos-B");
	if (IS_ERR(s2))
		...
1396
}
1397

1398 1399
foo_switch()
{
1400
	/* Enable on position A */
1401 1402 1403
	ret = pinctrl_select_state(s1);
	if (ret < 0)
	    ...
1404

1405
	...
1406 1407

	/* Enable on position B */
1408 1409 1410 1411
	ret = pinctrl_select_state(s2);
	if (ret < 0)
	    ...

1412 1413 1414
	...
}

1415 1416 1417
The above has to be done from process context. The reservation of the pins
will be done when the state is activated, so in effect one specific pin
can be used by different functions at different times on a running system.