Root/
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 datasheet |
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 the 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 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 retrieve a pin number. After |
377 | that, the subsystem passes it on to the pin control driver, so the driver |
378 | will get a 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 through 63 assigned |
434 | to 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 bottom 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 pin 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_set_mux(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 | struct pinmux_ops foo_pmxops = { |
715 | .get_functions_count = foo_get_functions_count, |
716 | .get_function_name = foo_get_fname, |
717 | .get_function_groups = foo_get_groups, |
718 | .set_mux = foo_set_mux, |
719 | }; |
720 | |
721 | /* Pinmux operations are handled by some pin controller */ |
722 | static struct pinctrl_desc foo_desc = { |
723 | ... |
724 | .pctlops = &foo_pctrl_ops, |
725 | .pmxops = &foo_pmxops, |
726 | }; |
727 | |
728 | In the example activating muxing 0 and 1 at the same time setting bits |
729 | 0 and 1, uses one pin in common so they would collide. |
730 | |
731 | The beauty of the pinmux subsystem is that since it keeps track of all |
732 | pins and who is using them, it will already have denied an impossible |
733 | request like that, so the driver does not need to worry about such |
734 | things - when it gets a selector passed in, the pinmux subsystem makes |
735 | sure no other device or GPIO assignment is already using the selected |
736 | pins. Thus bits 0 and 1 in the control register will never be set at the |
737 | same time. |
738 | |
739 | All the above functions are mandatory to implement for a pinmux driver. |
740 | |
741 | |
742 | Pin control interaction with the GPIO subsystem |
743 | =============================================== |
744 | |
745 | Note that the following implies that the use case is to use a certain pin |
746 | from the Linux kernel using the API in <linux/gpio.h> with gpio_request() |
747 | and similar functions. There are cases where you may be using something |
748 | that your datasheet calls "GPIO mode", but actually is just an electrical |
749 | configuration for a certain device. See the section below named |
750 | "GPIO mode pitfalls" for more details on this scenario. |
751 | |
752 | The public pinmux API contains two functions named pinctrl_request_gpio() |
753 | and pinctrl_free_gpio(). These two functions shall *ONLY* be called from |
754 | gpiolib-based drivers as part of their gpio_request() and |
755 | gpio_free() semantics. Likewise the pinctrl_gpio_direction_[input|output] |
756 | shall only be called from within respective gpio_direction_[input|output] |
757 | gpiolib implementation. |
758 | |
759 | NOTE that platforms and individual drivers shall *NOT* request GPIO pins to be |
760 | controlled e.g. muxed in. Instead, implement a proper gpiolib driver and have |
761 | that driver request proper muxing and other control for its pins. |
762 | |
763 | The function list could become long, especially if you can convert every |
764 | individual pin into a GPIO pin independent of any other pins, and then try |
765 | the approach to define every pin as a function. |
766 | |
767 | In this case, the function array would become 64 entries for each GPIO |
768 | setting and then the device functions. |
769 | |
770 | For this reason there are two functions a pin control driver can implement |
771 | to enable only GPIO on an individual pin: .gpio_request_enable() and |
772 | .gpio_disable_free(). |
773 | |
774 | This function will pass in the affected GPIO range identified by the pin |
775 | controller core, so you know which GPIO pins are being affected by the request |
776 | operation. |
777 | |
778 | If your driver needs to have an indication from the framework of whether the |
779 | GPIO pin shall be used for input or output you can implement the |
780 | .gpio_set_direction() function. As described this shall be called from the |
781 | gpiolib driver and the affected GPIO range, pin offset and desired direction |
782 | will be passed along to this function. |
783 | |
784 | Alternatively to using these special functions, it is fully allowed to use |
785 | named functions for each GPIO pin, the pinctrl_request_gpio() will attempt to |
786 | obtain the function "gpioN" where "N" is the global GPIO pin number if no |
787 | special GPIO-handler is registered. |
788 | |
789 | |
790 | GPIO mode pitfalls |
791 | ================== |
792 | |
793 | Due to the naming conventions used by hardware engineers, where "GPIO" |
794 | is taken to mean different things than what the kernel does, the developer |
795 | may be confused by a datasheet talking about a pin being possible to set |
796 | into "GPIO mode". It appears that what hardware engineers mean with |
797 | "GPIO mode" is not necessarily the use case that is implied in the kernel |
798 | interface <linux/gpio.h>: a pin that you grab from kernel code and then |
799 | either listen for input or drive high/low to assert/deassert some |
800 | external line. |
801 | |
802 | Rather hardware engineers think that "GPIO mode" means that you can |
803 | software-control a few electrical properties of the pin that you would |
804 | not be able to control if the pin was in some other mode, such as muxed in |
805 | for a device. |
806 | |
807 | The GPIO portions of a pin and its relation to a certain pin controller |
808 | configuration and muxing logic can be constructed in several ways. Here |
809 | are two examples: |
810 | |
811 | (A) |
812 | pin config |
813 | logic regs |
814 | | +- SPI |
815 | Physical pins --- pad --- pinmux -+- I2C |
816 | | +- mmc |
817 | | +- GPIO |
818 | pin |
819 | multiplex |
820 | logic regs |
821 | |
822 | Here some electrical properties of the pin can be configured no matter |
823 | whether the pin is used for GPIO or not. If you multiplex a GPIO onto a |
824 | pin, you can also drive it high/low from "GPIO" registers. |
825 | Alternatively, the pin can be controlled by a certain peripheral, while |
826 | still applying desired pin config properties. GPIO functionality is thus |
827 | orthogonal to any other device using the pin. |
828 | |
829 | In this arrangement the registers for the GPIO portions of the pin controller, |
830 | or the registers for the GPIO hardware module are likely to reside in a |
831 | separate memory range only intended for GPIO driving, and the register |
832 | range dealing with pin config and pin multiplexing get placed into a |
833 | different memory range and a separate section of the data sheet. |
834 | |
835 | (B) |
836 | |
837 | pin config |
838 | logic regs |
839 | | +- SPI |
840 | Physical pins --- pad --- pinmux -+- I2C |
841 | | | +- mmc |
842 | | | |
843 | GPIO pin |
844 | multiplex |
845 | logic regs |
846 | |
847 | In this arrangement, the GPIO functionality can always be enabled, such that |
848 | e.g. a GPIO input can be used to "spy" on the SPI/I2C/MMC signal while it is |
849 | pulsed out. It is likely possible to disrupt the traffic on the pin by doing |
850 | wrong things on the GPIO block, as it is never really disconnected. It is |
851 | possible that the GPIO, pin config and pin multiplex registers are placed into |
852 | the same memory range and the same section of the data sheet, although that |
853 | need not be the case. |
854 | |
855 | From a kernel point of view, however, these are different aspects of the |
856 | hardware and shall be put into different subsystems: |
857 | |
858 | - Registers (or fields within registers) that control electrical |
859 | properties of the pin such as biasing and drive strength should be |
860 | exposed through the pinctrl subsystem, as "pin configuration" settings. |
861 | |
862 | - Registers (or fields within registers) that control muxing of signals |
863 | from various other HW blocks (e.g. I2C, MMC, or GPIO) onto pins should |
864 | be exposed through the pinctrl subsystem, as mux functions. |
865 | |
866 | - Registers (or fields within registers) that control GPIO functionality |
867 | such as setting a GPIO's output value, reading a GPIO's input value, or |
868 | setting GPIO pin direction should be exposed through the GPIO subsystem, |
869 | and if they also support interrupt capabilities, through the irqchip |
870 | abstraction. |
871 | |
872 | Depending on the exact HW register design, some functions exposed by the |
873 | GPIO subsystem may call into the pinctrl subsystem in order to |
874 | co-ordinate register settings across HW modules. In particular, this may |
875 | be needed for HW with separate GPIO and pin controller HW modules, where |
876 | e.g. GPIO direction is determined by a register in the pin controller HW |
877 | module rather than the GPIO HW module. |
878 | |
879 | Electrical properties of the pin such as biasing and drive strength |
880 | may be placed at some pin-specific register in all cases or as part |
881 | of the GPIO register in case (B) especially. This doesn't mean that such |
882 | properties necessarily pertain to what the Linux kernel calls "GPIO". |
883 | |
884 | Example: a pin is usually muxed in to be used as a UART TX line. But during |
885 | system sleep, we need to put this pin into "GPIO mode" and ground it. |
886 | |
887 | If you make a 1-to-1 map to the GPIO subsystem for this pin, you may start |
888 | to think that you need to come up with something really complex, that the |
889 | pin shall be used for UART TX and GPIO at the same time, that you will grab |
890 | a pin control handle and set it to a certain state to enable UART TX to be |
891 | muxed in, then twist it over to GPIO mode and use gpio_direction_output() |
892 | to drive it low during sleep, then mux it over to UART TX again when you |
893 | wake up and maybe even gpio_request/gpio_free as part of this cycle. This |
894 | all gets very complicated. |
895 | |
896 | The solution is to not think that what the datasheet calls "GPIO mode" |
897 | has to be handled by the <linux/gpio.h> interface. Instead view this as |
898 | a certain pin config setting. Look in e.g. <linux/pinctrl/pinconf-generic.h> |
899 | and you find this in the documentation: |
900 | |
901 | PIN_CONFIG_OUTPUT: this will configure the pin in output, use argument |
902 | 1 to indicate high level, argument 0 to indicate low level. |
903 | |
904 | So it is perfectly possible to push a pin into "GPIO mode" and drive the |
905 | line low as part of the usual pin control map. So for example your UART |
906 | driver may look like this: |
907 | |
908 | #include <linux/pinctrl/consumer.h> |
909 | |
910 | struct pinctrl *pinctrl; |
911 | struct pinctrl_state *pins_default; |
912 | struct pinctrl_state *pins_sleep; |
913 | |
914 | pins_default = pinctrl_lookup_state(uap->pinctrl, PINCTRL_STATE_DEFAULT); |
915 | pins_sleep = pinctrl_lookup_state(uap->pinctrl, PINCTRL_STATE_SLEEP); |
916 | |
917 | /* Normal mode */ |
918 | retval = pinctrl_select_state(pinctrl, pins_default); |
919 | /* Sleep mode */ |
920 | retval = pinctrl_select_state(pinctrl, pins_sleep); |
921 | |
922 | And your machine configuration may look like this: |
923 | -------------------------------------------------- |
924 | |
925 | static unsigned long uart_default_mode[] = { |
926 | PIN_CONF_PACKED(PIN_CONFIG_DRIVE_PUSH_PULL, 0), |
927 | }; |
928 | |
929 | static unsigned long uart_sleep_mode[] = { |
930 | PIN_CONF_PACKED(PIN_CONFIG_OUTPUT, 0), |
931 | }; |
932 | |
933 | static struct pinctrl_map pinmap[] __initdata = { |
934 | PIN_MAP_MUX_GROUP("uart", PINCTRL_STATE_DEFAULT, "pinctrl-foo", |
935 | "u0_group", "u0"), |
936 | PIN_MAP_CONFIGS_PIN("uart", PINCTRL_STATE_DEFAULT, "pinctrl-foo", |
937 | "UART_TX_PIN", uart_default_mode), |
938 | PIN_MAP_MUX_GROUP("uart", PINCTRL_STATE_SLEEP, "pinctrl-foo", |
939 | "u0_group", "gpio-mode"), |
940 | PIN_MAP_CONFIGS_PIN("uart", PINCTRL_STATE_SLEEP, "pinctrl-foo", |
941 | "UART_TX_PIN", uart_sleep_mode), |
942 | }; |
943 | |
944 | foo_init(void) { |
945 | pinctrl_register_mappings(pinmap, ARRAY_SIZE(pinmap)); |
946 | } |
947 | |
948 | Here the pins we want to control are in the "u0_group" and there is some |
949 | function called "u0" that can be enabled on this group of pins, and then |
950 | everything is UART business as usual. But there is also some function |
951 | named "gpio-mode" that can be mapped onto the same pins to move them into |
952 | GPIO mode. |
953 | |
954 | This will give the desired effect without any bogus interaction with the |
955 | GPIO subsystem. It is just an electrical configuration used by that device |
956 | when going to sleep, it might imply that the pin is set into something the |
957 | datasheet calls "GPIO mode", but that is not the point: it is still used |
958 | by that UART device to control the pins that pertain to that very UART |
959 | driver, putting them into modes needed by the UART. GPIO in the Linux |
960 | kernel sense are just some 1-bit line, and is a different use case. |
961 | |
962 | How the registers are poked to attain the push or pull, and output low |
963 | configuration and the muxing of the "u0" or "gpio-mode" group onto these |
964 | pins is a question for the driver. |
965 | |
966 | Some datasheets will be more helpful and refer to the "GPIO mode" as |
967 | "low power mode" rather than anything to do with GPIO. This often means |
968 | the same thing electrically speaking, but in this latter case the |
969 | software engineers will usually quickly identify that this is some |
970 | specific muxing or configuration rather than anything related to the GPIO |
971 | API. |
972 | |
973 | |
974 | Board/machine configuration |
975 | ================================== |
976 | |
977 | Boards and machines define how a certain complete running system is put |
978 | together, including how GPIOs and devices are muxed, how regulators are |
979 | constrained and how the clock tree looks. Of course pinmux settings are also |
980 | part of this. |
981 | |
982 | A pin controller configuration for a machine looks pretty much like a simple |
983 | regulator configuration, so for the example array above we want to enable i2c |
984 | and spi on the second function mapping: |
985 | |
986 | #include <linux/pinctrl/machine.h> |
987 | |
988 | static const struct pinctrl_map mapping[] __initconst = { |
989 | { |
990 | .dev_name = "foo-spi.0", |
991 | .name = PINCTRL_STATE_DEFAULT, |
992 | .type = PIN_MAP_TYPE_MUX_GROUP, |
993 | .ctrl_dev_name = "pinctrl-foo", |
994 | .data.mux.function = "spi0", |
995 | }, |
996 | { |
997 | .dev_name = "foo-i2c.0", |
998 | .name = PINCTRL_STATE_DEFAULT, |
999 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1000 | .ctrl_dev_name = "pinctrl-foo", |
1001 | .data.mux.function = "i2c0", |
1002 | }, |
1003 | { |
1004 | .dev_name = "foo-mmc.0", |
1005 | .name = PINCTRL_STATE_DEFAULT, |
1006 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1007 | .ctrl_dev_name = "pinctrl-foo", |
1008 | .data.mux.function = "mmc0", |
1009 | }, |
1010 | }; |
1011 | |
1012 | The dev_name here matches to the unique device name that can be used to look |
1013 | up the device struct (just like with clockdev or regulators). The function name |
1014 | must match a function provided by the pinmux driver handling this pin range. |
1015 | |
1016 | As you can see we may have several pin controllers on the system and thus |
1017 | we need to specify which one of them contains the functions we wish to map. |
1018 | |
1019 | You register this pinmux mapping to the pinmux subsystem by simply: |
1020 | |
1021 | ret = pinctrl_register_mappings(mapping, ARRAY_SIZE(mapping)); |
1022 | |
1023 | Since the above construct is pretty common there is a helper macro to make |
1024 | it even more compact which assumes you want to use pinctrl-foo and position |
1025 | 0 for mapping, for example: |
1026 | |
1027 | static struct pinctrl_map mapping[] __initdata = { |
1028 | PIN_MAP_MUX_GROUP("foo-i2c.o", PINCTRL_STATE_DEFAULT, "pinctrl-foo", NULL, "i2c0"), |
1029 | }; |
1030 | |
1031 | The mapping table may also contain pin configuration entries. It's common for |
1032 | each pin/group to have a number of configuration entries that affect it, so |
1033 | the table entries for configuration reference an array of config parameters |
1034 | and values. An example using the convenience macros is shown below: |
1035 | |
1036 | static unsigned long i2c_grp_configs[] = { |
1037 | FOO_PIN_DRIVEN, |
1038 | FOO_PIN_PULLUP, |
1039 | }; |
1040 | |
1041 | static unsigned long i2c_pin_configs[] = { |
1042 | FOO_OPEN_COLLECTOR, |
1043 | FOO_SLEW_RATE_SLOW, |
1044 | }; |
1045 | |
1046 | static struct pinctrl_map mapping[] __initdata = { |
1047 | PIN_MAP_MUX_GROUP("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0", "i2c0"), |
1048 | PIN_MAP_CONFIGS_GROUP("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0", i2c_grp_configs), |
1049 | PIN_MAP_CONFIGS_PIN("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0scl", i2c_pin_configs), |
1050 | PIN_MAP_CONFIGS_PIN("foo-i2c.0", PINCTRL_STATE_DEFAULT, "pinctrl-foo", "i2c0sda", i2c_pin_configs), |
1051 | }; |
1052 | |
1053 | Finally, some devices expect the mapping table to contain certain specific |
1054 | named states. When running on hardware that doesn't need any pin controller |
1055 | configuration, the mapping table must still contain those named states, in |
1056 | order to explicitly indicate that the states were provided and intended to |
1057 | be empty. Table entry macro PIN_MAP_DUMMY_STATE serves the purpose of defining |
1058 | a named state without causing any pin controller to be programmed: |
1059 | |
1060 | static struct pinctrl_map mapping[] __initdata = { |
1061 | PIN_MAP_DUMMY_STATE("foo-i2c.0", PINCTRL_STATE_DEFAULT), |
1062 | }; |
1063 | |
1064 | |
1065 | Complex mappings |
1066 | ================ |
1067 | |
1068 | As it is possible to map a function to different groups of pins an optional |
1069 | .group can be specified like this: |
1070 | |
1071 | ... |
1072 | { |
1073 | .dev_name = "foo-spi.0", |
1074 | .name = "spi0-pos-A", |
1075 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1076 | .ctrl_dev_name = "pinctrl-foo", |
1077 | .function = "spi0", |
1078 | .group = "spi0_0_grp", |
1079 | }, |
1080 | { |
1081 | .dev_name = "foo-spi.0", |
1082 | .name = "spi0-pos-B", |
1083 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1084 | .ctrl_dev_name = "pinctrl-foo", |
1085 | .function = "spi0", |
1086 | .group = "spi0_1_grp", |
1087 | }, |
1088 | ... |
1089 | |
1090 | This example mapping is used to switch between two positions for spi0 at |
1091 | runtime, as described further below under the heading "Runtime pinmuxing". |
1092 | |
1093 | Further it is possible for one named state to affect the muxing of several |
1094 | groups of pins, say for example in the mmc0 example above, where you can |
1095 | additively expand the mmc0 bus from 2 to 4 to 8 pins. If we want to use all |
1096 | three groups for a total of 2+2+4 = 8 pins (for an 8-bit MMC bus as is the |
1097 | case), we define a mapping like this: |
1098 | |
1099 | ... |
1100 | { |
1101 | .dev_name = "foo-mmc.0", |
1102 | .name = "2bit" |
1103 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1104 | .ctrl_dev_name = "pinctrl-foo", |
1105 | .function = "mmc0", |
1106 | .group = "mmc0_1_grp", |
1107 | }, |
1108 | { |
1109 | .dev_name = "foo-mmc.0", |
1110 | .name = "4bit" |
1111 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1112 | .ctrl_dev_name = "pinctrl-foo", |
1113 | .function = "mmc0", |
1114 | .group = "mmc0_1_grp", |
1115 | }, |
1116 | { |
1117 | .dev_name = "foo-mmc.0", |
1118 | .name = "4bit" |
1119 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1120 | .ctrl_dev_name = "pinctrl-foo", |
1121 | .function = "mmc0", |
1122 | .group = "mmc0_2_grp", |
1123 | }, |
1124 | { |
1125 | .dev_name = "foo-mmc.0", |
1126 | .name = "8bit" |
1127 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1128 | .ctrl_dev_name = "pinctrl-foo", |
1129 | .function = "mmc0", |
1130 | .group = "mmc0_1_grp", |
1131 | }, |
1132 | { |
1133 | .dev_name = "foo-mmc.0", |
1134 | .name = "8bit" |
1135 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1136 | .ctrl_dev_name = "pinctrl-foo", |
1137 | .function = "mmc0", |
1138 | .group = "mmc0_2_grp", |
1139 | }, |
1140 | { |
1141 | .dev_name = "foo-mmc.0", |
1142 | .name = "8bit" |
1143 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1144 | .ctrl_dev_name = "pinctrl-foo", |
1145 | .function = "mmc0", |
1146 | .group = "mmc0_3_grp", |
1147 | }, |
1148 | ... |
1149 | |
1150 | The result of grabbing this mapping from the device with something like |
1151 | this (see next paragraph): |
1152 | |
1153 | p = devm_pinctrl_get(dev); |
1154 | s = pinctrl_lookup_state(p, "8bit"); |
1155 | ret = pinctrl_select_state(p, s); |
1156 | |
1157 | or more simply: |
1158 | |
1159 | p = devm_pinctrl_get_select(dev, "8bit"); |
1160 | |
1161 | Will be that you activate all the three bottom records in the mapping at |
1162 | once. Since they share the same name, pin controller device, function and |
1163 | device, and since we allow multiple groups to match to a single device, they |
1164 | all get selected, and they all get enabled and disable simultaneously by the |
1165 | pinmux core. |
1166 | |
1167 | |
1168 | Pin control requests from drivers |
1169 | ================================= |
1170 | |
1171 | When a device driver is about to probe the device core will automatically |
1172 | attempt to issue pinctrl_get_select_default() on these devices. |
1173 | This way driver writers do not need to add any of the boilerplate code |
1174 | of the type found below. However when doing fine-grained state selection |
1175 | and not using the "default" state, you may have to do some device driver |
1176 | handling of the pinctrl handles and states. |
1177 | |
1178 | So if you just want to put the pins for a certain device into the default |
1179 | state and be done with it, there is nothing you need to do besides |
1180 | providing the proper mapping table. The device core will take care of |
1181 | the rest. |
1182 | |
1183 | Generally it is discouraged to let individual drivers get and enable pin |
1184 | control. So if possible, handle the pin control in platform code or some other |
1185 | place where you have access to all the affected struct device * pointers. In |
1186 | some cases where a driver needs to e.g. switch between different mux mappings |
1187 | at runtime this is not possible. |
1188 | |
1189 | A typical case is if a driver needs to switch bias of pins from normal |
1190 | operation and going to sleep, moving from the PINCTRL_STATE_DEFAULT to |
1191 | PINCTRL_STATE_SLEEP at runtime, re-biasing or even re-muxing pins to save |
1192 | current in sleep mode. |
1193 | |
1194 | A driver may request a certain control state to be activated, usually just the |
1195 | default state like this: |
1196 | |
1197 | #include <linux/pinctrl/consumer.h> |
1198 | |
1199 | struct foo_state { |
1200 | struct pinctrl *p; |
1201 | struct pinctrl_state *s; |
1202 | ... |
1203 | }; |
1204 | |
1205 | foo_probe() |
1206 | { |
1207 | /* Allocate a state holder named "foo" etc */ |
1208 | struct foo_state *foo = ...; |
1209 | |
1210 | foo->p = devm_pinctrl_get(&device); |
1211 | if (IS_ERR(foo->p)) { |
1212 | /* FIXME: clean up "foo" here */ |
1213 | return PTR_ERR(foo->p); |
1214 | } |
1215 | |
1216 | foo->s = pinctrl_lookup_state(foo->p, PINCTRL_STATE_DEFAULT); |
1217 | if (IS_ERR(foo->s)) { |
1218 | /* FIXME: clean up "foo" here */ |
1219 | return PTR_ERR(s); |
1220 | } |
1221 | |
1222 | ret = pinctrl_select_state(foo->s); |
1223 | if (ret < 0) { |
1224 | /* FIXME: clean up "foo" here */ |
1225 | return ret; |
1226 | } |
1227 | } |
1228 | |
1229 | This get/lookup/select/put sequence can just as well be handled by bus drivers |
1230 | if you don't want each and every driver to handle it and you know the |
1231 | arrangement on your bus. |
1232 | |
1233 | The semantics of the pinctrl APIs are: |
1234 | |
1235 | - pinctrl_get() is called in process context to obtain a handle to all pinctrl |
1236 | information for a given client device. It will allocate a struct from the |
1237 | kernel memory to hold the pinmux state. All mapping table parsing or similar |
1238 | slow operations take place within this API. |
1239 | |
1240 | - devm_pinctrl_get() is a variant of pinctrl_get() that causes pinctrl_put() |
1241 | to be called automatically on the retrieved pointer when the associated |
1242 | device is removed. It is recommended to use this function over plain |
1243 | pinctrl_get(). |
1244 | |
1245 | - pinctrl_lookup_state() is called in process context to obtain a handle to a |
1246 | specific state for a client device. This operation may be slow, too. |
1247 | |
1248 | - pinctrl_select_state() programs pin controller hardware according to the |
1249 | definition of the state as given by the mapping table. In theory, this is a |
1250 | fast-path operation, since it only involved blasting some register settings |
1251 | into hardware. However, note that some pin controllers may have their |
1252 | registers on a slow/IRQ-based bus, so client devices should not assume they |
1253 | can call pinctrl_select_state() from non-blocking contexts. |
1254 | |
1255 | - pinctrl_put() frees all information associated with a pinctrl handle. |
1256 | |
1257 | - devm_pinctrl_put() is a variant of pinctrl_put() that may be used to |
1258 | explicitly destroy a pinctrl object returned by devm_pinctrl_get(). |
1259 | However, use of this function will be rare, due to the automatic cleanup |
1260 | that will occur even without calling it. |
1261 | |
1262 | pinctrl_get() must be paired with a plain pinctrl_put(). |
1263 | pinctrl_get() may not be paired with devm_pinctrl_put(). |
1264 | devm_pinctrl_get() can optionally be paired with devm_pinctrl_put(). |
1265 | devm_pinctrl_get() may not be paired with plain pinctrl_put(). |
1266 | |
1267 | Usually the pin control core handled the get/put pair and call out to the |
1268 | device drivers bookkeeping operations, like checking available functions and |
1269 | the associated pins, whereas the enable/disable pass on to the pin controller |
1270 | driver which takes care of activating and/or deactivating the mux setting by |
1271 | quickly poking some registers. |
1272 | |
1273 | The pins are allocated for your device when you issue the devm_pinctrl_get() |
1274 | call, after this you should be able to see this in the debugfs listing of all |
1275 | pins. |
1276 | |
1277 | NOTE: the pinctrl system will return -EPROBE_DEFER if it cannot find the |
1278 | requested pinctrl handles, for example if the pinctrl driver has not yet |
1279 | registered. Thus make sure that the error path in your driver gracefully |
1280 | cleans up and is ready to retry the probing later in the startup process. |
1281 | |
1282 | |
1283 | Drivers needing both pin control and GPIOs |
1284 | ========================================== |
1285 | |
1286 | Again, it is discouraged to let drivers lookup and select pin control states |
1287 | themselves, but again sometimes this is unavoidable. |
1288 | |
1289 | So say that your driver is fetching its resources like this: |
1290 | |
1291 | #include <linux/pinctrl/consumer.h> |
1292 | #include <linux/gpio.h> |
1293 | |
1294 | struct pinctrl *pinctrl; |
1295 | int gpio; |
1296 | |
1297 | pinctrl = devm_pinctrl_get_select_default(&dev); |
1298 | gpio = devm_gpio_request(&dev, 14, "foo"); |
1299 | |
1300 | Here we first request a certain pin state and then request GPIO 14 to be |
1301 | used. If you're using the subsystems orthogonally like this, you should |
1302 | nominally always get your pinctrl handle and select the desired pinctrl |
1303 | state BEFORE requesting the GPIO. This is a semantic convention to avoid |
1304 | situations that can be electrically unpleasant, you will certainly want to |
1305 | mux in and bias pins in a certain way before the GPIO subsystems starts to |
1306 | deal with them. |
1307 | |
1308 | The above can be hidden: using the device core, the pinctrl core may be |
1309 | setting up the config and muxing for the pins right before the device is |
1310 | probing, nevertheless orthogonal to the GPIO subsystem. |
1311 | |
1312 | But there are also situations where it makes sense for the GPIO subsystem |
1313 | to communicate directly with the pinctrl subsystem, using the latter as a |
1314 | back-end. This is when the GPIO driver may call out to the functions |
1315 | described in the section "Pin control interaction with the GPIO subsystem" |
1316 | above. This only involves per-pin multiplexing, and will be completely |
1317 | hidden behind the gpio_*() function namespace. In this case, the driver |
1318 | need not interact with the pin control subsystem at all. |
1319 | |
1320 | If a pin control driver and a GPIO driver is dealing with the same pins |
1321 | and the use cases involve multiplexing, you MUST implement the pin controller |
1322 | as a back-end for the GPIO driver like this, unless your hardware design |
1323 | is such that the GPIO controller can override the pin controller's |
1324 | multiplexing state through hardware without the need to interact with the |
1325 | pin control system. |
1326 | |
1327 | |
1328 | System pin control hogging |
1329 | ========================== |
1330 | |
1331 | Pin control map entries can be hogged by the core when the pin controller |
1332 | is registered. This means that the core will attempt to call pinctrl_get(), |
1333 | lookup_state() and select_state() on it immediately after the pin control |
1334 | device has been registered. |
1335 | |
1336 | This occurs for mapping table entries where the client device name is equal |
1337 | to the pin controller device name, and the state name is PINCTRL_STATE_DEFAULT. |
1338 | |
1339 | { |
1340 | .dev_name = "pinctrl-foo", |
1341 | .name = PINCTRL_STATE_DEFAULT, |
1342 | .type = PIN_MAP_TYPE_MUX_GROUP, |
1343 | .ctrl_dev_name = "pinctrl-foo", |
1344 | .function = "power_func", |
1345 | }, |
1346 | |
1347 | Since it may be common to request the core to hog a few always-applicable |
1348 | mux settings on the primary pin controller, there is a convenience macro for |
1349 | this: |
1350 | |
1351 | PIN_MAP_MUX_GROUP_HOG_DEFAULT("pinctrl-foo", NULL /* group */, "power_func") |
1352 | |
1353 | This gives the exact same result as the above construction. |
1354 | |
1355 | |
1356 | Runtime pinmuxing |
1357 | ================= |
1358 | |
1359 | It is possible to mux a certain function in and out at runtime, say to move |
1360 | an SPI port from one set of pins to another set of pins. Say for example for |
1361 | spi0 in the example above, we expose two different groups of pins for the same |
1362 | function, but with different named in the mapping as described under |
1363 | "Advanced mapping" above. So that for an SPI device, we have two states named |
1364 | "pos-A" and "pos-B". |
1365 | |
1366 | This snippet first muxes the function in the pins defined by group A, enables |
1367 | it, disables and releases it, and muxes it in on the pins defined by group B: |
1368 | |
1369 | #include <linux/pinctrl/consumer.h> |
1370 | |
1371 | struct pinctrl *p; |
1372 | struct pinctrl_state *s1, *s2; |
1373 | |
1374 | foo_probe() |
1375 | { |
1376 | /* Setup */ |
1377 | p = devm_pinctrl_get(&device); |
1378 | if (IS_ERR(p)) |
1379 | ... |
1380 | |
1381 | s1 = pinctrl_lookup_state(foo->p, "pos-A"); |
1382 | if (IS_ERR(s1)) |
1383 | ... |
1384 | |
1385 | s2 = pinctrl_lookup_state(foo->p, "pos-B"); |
1386 | if (IS_ERR(s2)) |
1387 | ... |
1388 | } |
1389 | |
1390 | foo_switch() |
1391 | { |
1392 | /* Enable on position A */ |
1393 | ret = pinctrl_select_state(s1); |
1394 | if (ret < 0) |
1395 | ... |
1396 | |
1397 | ... |
1398 | |
1399 | /* Enable on position B */ |
1400 | ret = pinctrl_select_state(s2); |
1401 | if (ret < 0) |
1402 | ... |
1403 | |
1404 | ... |
1405 | } |
1406 | |
1407 | The above has to be done from process context. The reservation of the pins |
1408 | will be done when the state is activated, so in effect one specific pin |
1409 | can be used by different functions at different times on a running system. |
1410 |
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