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 The intention is to also deal with: - Software-controlled biasing and driving mode specific pins, such as pull-up/down, open drain etc, load capacitance configuration when controlled by software, etc. 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, set drive strength etc for individual pins or groups of pins. 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. When a PIN CONTROLLER is instatiated, it will register a descriptor to the 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 const struct pinctrl_pin_desc __refdata foo_pins[] = { PINCTRL_PIN(0, "A1"), PINCTRL_PIN(1, "A2"), PINCTRL_PIN(2, "A3"), ... PINCTRL_PIN(61, "H6"), PINCTRL_PIN(62, "H7"), PINCTRL_PIN(63, "H8"), }; static struct pinctrl_desc foo_desc = { .name = "foo", .pins = foo_pins, .npins = ARRAY_SIZE(foo_pins), .maxpin = 63, .owner = THIS_MODULE, }; int __init foo_probe(void) { struct pinctrl_dev *pctl; pctl = pinctrl_register(&foo_desc, , NULL); if (IS_ERR(pctl)) pr_err("could not register foo pin driver\n"); } Pins usually have fancier names than this. You can find these in the dataheet 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 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 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 struct foo_group { const char *name; const unsigned int *pins; const unsigned num_pins; }; static unsigned int spi0_pins[] = { 0, 8, 16, 24 }; static unsigned int i2c0_pins[] = { 24, 25 }; 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), }, }; static int foo_list_groups(struct pinctrl_dev *pctldev, unsigned selector) { if (selector >= ARRAY_SIZE(foo_groups)) return -EINVAL; return 0; } 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 = { .list_groups = foo_list_groups, .get_group_name = foo_get_group_name, .get_group_pins = foo_get_group_pins, }; static struct pinctrl_desc foo_desc = { ... .pctlops = &foo_pctrl_ops, }; The pin control subsystem will call the .list_groups() function repeatedly beginning on 0 until it returns non-zero to determine legal selectors, then it will call the other functions 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. 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. Since the pin controller subsystem have 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 modeled as a struct gpio_chip) any number of GPIO ranges can be added to a pin controller instance like this: 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, .npins = 16, .gc = &chip_a; }; static struct pinctrl_gpio_range gpio_range_a = { .name = "chip b", .id = 0, .base = 48, .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 GPIO chips. Chip a has 16 pins and chip b has 8 pins. They are mapped in the global GPIO pin space at: chip a: [32 .. 47] chip b: [48 .. 55] When GPIO-specific functions in the pin control subsystem are called, these ranges will be used to look up the apropriate pin controller by inspecting 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 controller subsystem will subtract the range's .base offset from the passed in gpio pin number, and pass that on to the pin control driver, so the driver will get an offset into its handled number range. Further it is also passed the range ID value, so that the pin controller knows which range it should deal with. For example: if a user issues pinctrl_gpio_set_foo(50), the pin control subsystem will find that the second range on this pin controller matches, subtract the base 48 and call the pinctrl_driver_gpio_set_foo(pinctrl, range, 2) where the latter function has this signature: int pinctrl_driver_gpio_set_foo(struct pinctrl_dev *pctldev, struct pinctrl_gpio_range *rangeid, unsigned offset); Now the driver knows that we want to do some GPIO-specific operation on the second GPIO range handled by "chip b", at offset 2 in that specific range. (If the GPIO subsystem is ever refactored to use a local per-GPIO controller pin space, this mapping will need to be augmented accordingly.) 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. The example 8x8 PGA package above will have pin numbers 0 thru 63 assigned to its physical pins. It will name the pins { A1, A2, A3 ... H6, H7, H8 } using 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 }. On the botton row at { A1, B1, C1, D1, E1, F1, G1, H1 } we have something 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, from the outside only the enumerators are known, and the driver core can: - Request the name of a function with a certain selector (>= 0) - A list of groups associated with a certain function - Request that a certain group in that list to be activated for a certain function 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} } Every map must be assigned a symbolic name, pin controller 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. The device name is present in map entries tied to specific devices. Maps without device names are referred to as SYSTEM pinmuxes, such as can be taken by the machine implementation on boot and not tied to any specific device. 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: We assume that the number possible function maps to pin groups is limited by the hardware. I.e. we assume that there is no system where any function can be mapped to any pin, like in a phone exchange. So the available pins groups for 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 (say for example infer electronic limitations due to load etc) to determine 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 optional. Usually the enable() and disable() functions are implemented, writing values into some certain registers to activate a certain mux setting for a certain pin. 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 #include 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), }, }; static int foo_list_groups(struct pinctrl_dev *pctldev, unsigned selector) { if (selector >= ARRAY_SIZE(foo_groups)) return -EINVAL; return 0; } 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 = { .list_groups = foo_list_groups, .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; }; static const char * const spi0_groups[] = { "spi0_1_grp" }; 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), }, }; int foo_list_funcs(struct pinctrl_dev *pctldev, unsigned selector) { if (selector >= ARRAY_SIZE(foo_functions)) return -EINVAL; return 0; } const char *foo_get_fname(struct pinctrl_dev *pctldev, unsigned selector) { return myfuncs[selector].name; } 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; } int foo_enable(struct pinctrl_dev *pctldev, unsigned selector, unsigned group) { u8 regbit = (1 << group); writeb((readb(MUX)|regbit), MUX) return 0; } int foo_disable(struct pinctrl_dev *pctldev, unsigned selector, unsigned group) { u8 regbit = (1 << group); writeb((readb(MUX) & ~(regbit)), MUX) return 0; } struct pinmux_ops foo_pmxops = { .list_functions = foo_list_funcs, .get_function_name = foo_get_fname, .get_function_groups = foo_get_groups, .enable = foo_enable, .disable = foo_disable, }; /* 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. Pinmux interaction with the GPIO subsystem ========================================== 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. For this reason there is an additional function a pinmux driver can implement to enable only GPIO on an individual pin: .gpio_request_enable(). The same .free() function as for other functions is assumed to be usable also for GPIO pins. 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. Alternatively it is fully allowed to use named functions for each GPIO pin, the pinmux_request_gpio() will attempt to obtain the function "gpioN" where "N" is the global GPIO pin number if no special GPIO-handler is registered. Pinmux board/machine configuration ================================== 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. A pinmux config 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: #include static struct pinmux_map pmx_mapping[] = { { .ctrl_dev_name = "pinctrl.0", .function = "spi0", .dev_name = "foo-spi.0", }, { .ctrl_dev_name = "pinctrl.0", .function = "i2c0", .dev_name = "foo-i2c.0", }, { .ctrl_dev_name = "pinctrl.0", .function = "mmc0", .dev_name = "foo-mmc.0", }, }; 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 we need to specify which one of them that contain the functions we wish to map. The map can also use struct device * directly, so there is no inherent need to use strings to specify .dev_name or .ctrl_dev_name, these are for the situation where you do not have a handle to the struct device *, for example if they are not yet instantiated or cumbersome to obtain. You register this pinmux mapping to the pinmux subsystem by simply: ret = pinmux_register_mappings(&pmx_mapping, ARRAY_SIZE(pmx_mapping)); Since the above construct is pretty common there is a helper macro to make it even more compact which assumes you want to use pinctrl.0 and position 0 for mapping, for example: static struct pinmux_map pmx_mapping[] = { PINMUX_MAP_PRIMARY("I2CMAP", "i2c0", "foo-i2c.0"), }; Complex mappings ================ As it is possible to map a function to different groups of pins an optional .group can be specified like this: ... { .name = "spi0-pos-A", .ctrl_dev_name = "pinctrl.0", .function = "spi0", .group = "spi0_0_grp", .dev_name = "foo-spi.0", }, { .name = "spi0-pos-B", .ctrl_dev_name = "pinctrl.0", .function = "spi0", .group = "spi0_1_grp", .dev_name = "foo-spi.0", }, ... This example mapping is used to switch between two positions for spi0 at runtime, as described further below under the heading "Runtime pinmuxing". Further it is possible to match several groups of pins to the same function for a single device, say for example in the mmc0 example above, where you can 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: ... { .name "2bit" .ctrl_dev_name = "pinctrl.0", .function = "mmc0", .group = "mmc0_0_grp", .dev_name = "foo-mmc.0", }, { .name "4bit" .ctrl_dev_name = "pinctrl.0", .function = "mmc0", .group = "mmc0_0_grp", .dev_name = "foo-mmc.0", }, { .name "4bit" .ctrl_dev_name = "pinctrl.0", .function = "mmc0", .group = "mmc0_1_grp", .dev_name = "foo-mmc.0", }, { .name "8bit" .ctrl_dev_name = "pinctrl.0", .function = "mmc0", .group = "mmc0_0_grp", .dev_name = "foo-mmc.0", }, { .name "8bit" .ctrl_dev_name = "pinctrl.0", .function = "mmc0", .group = "mmc0_1_grp", .dev_name = "foo-mmc.0", }, { .name "8bit" .ctrl_dev_name = "pinctrl.0", .function = "mmc0", .group = "mmc0_2_grp", .dev_name = "foo-mmc.0", }, ... The result of grabbing this mapping from the device with something like this (see next paragraph): pmx = pinmux_get(&device, "8bit"); Will be that you activate all the three bottom records in the mapping at once. Since they share the same name, pin controller device, funcion and 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. Pinmux requests from drivers ============================ Generally it is discouraged to let individual drivers get and enable pinmuxes. So if possible, handle the pinmuxes 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 switch between different mux mappings at runtime this is not possible. A driver may request a certain mux to be activated, usually just the default mux like this: #include struct foo_state { struct pinmux *pmx; ... }; foo_probe() { /* Allocate a state holder named "state" etc */ struct pinmux pmx; pmx = pinmux_get(&device, NULL); if IS_ERR(pmx) return PTR_ERR(pmx); pinmux_enable(pmx); state->pmx = pmx; } foo_remove() { pinmux_disable(state->pmx); pinmux_put(state->pmx); } If you want to grab a specific mux mapping and not just the first one found for this device you can specify a specific mapping name, for example in the above example the second i2c0 setting: pinmux_get(&device, "spi0-pos-B"); This get/enable/disable/put sequence can just as well be handled by bus drivers if you don't want each and every driver to handle it and you know the arrangement on your bus. The semantics of the get/enable respective disable/put is as follows: - pinmux_get() is called in process context to reserve the pins affected with a certain mapping and set up the pinmux core and the driver. It will allocate a struct from the kernel memory to hold the pinmux state. - pinmux_enable()/pinmux_disable() is quick and can be called from fastpath (irq context) when you quickly want to set up/tear down the hardware muxing when running a device driver. Usually it will just poke some values into a register. - pinmux_disable() is called in process context to tear down the pin requests and release the state holder struct for the mux setting. Usually the pinmux core handled the get/put pair and call out to the device drivers bookkeeping operations, like checking available functions and the associated pins, whereas the enable/disable pass on to the pin controller driver which takes care of activating and/or deactivating the mux setting by quickly poking some registers. The pins are allocated for your device when you issue the pinmux_get() call, after this you should be able to see this in the debugfs listing of all pins. System pinmux hogging ===================== A system pinmux map entry, i.e. a pinmux setting that does not have a device associated with it, can be hogged by the core when the pin controller is registered. This means that the core will attempt to call pinmux_get() and pinmux_enable() on it immediately after the pin control device has been registered. This is enabled by simply setting the .hog_on_boot field in the map to true, like this: { .name "POWERMAP" .ctrl_dev_name = "pinctrl.0", .function = "power_func", .hog_on_boot = true, }, 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: PINMUX_MAP_PRIMARY_SYS_HOG("POWERMAP", "power_func") 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 "Advanced mapping" above. So we have two mappings named "spi0-pos-A" and "spi0-pos-B". This snippet first muxes the function in the pins defined by group A, enables it, disables and releases it, and muxes it in on the pins defined by group B: foo_switch() { struct pinmux pmx; /* Enable on position A */ pmx = pinmux_get(&device, "spi0-pos-A"); if IS_ERR(pmx) return PTR_ERR(pmx); pinmux_enable(pmx); /* This releases the pins again */ pinmux_disable(pmx); pinmux_put(pmx); /* Enable on position B */ pmx = pinmux_get(&device, "spi0-pos-B"); if IS_ERR(pmx) return PTR_ERR(pmx); pinmux_enable(pmx); ... } The above has to be done from process context.