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diff --git a/Documentation/pinctrl.txt b/Documentation/pinctrl.txt new file mode 100644 index 0000000..074da62 --- /dev/null +++ b/Documentation/pinctrl.txt @@ -0,0 +1,950 @@ +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 <linux/pinctrl/pinctrl.h> + +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, <PARENT>, 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 <linux/pinctrl/pinctrl.h> + +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, + const unsigned **pins, + unsigned *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 <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), + }, +}; + + +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 <linux/pinctrl/machine.h> + +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 <linux/pinctrl/pinmux.h> + +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. |