== Introduction == Hardware modules that control pin multiplexing or configuration parameters such as pull-up/down, tri-state, drive-strength etc are designated as pin controllers. Each pin controller must be represented as a node in device tree, just like any other hardware module. Hardware modules whose signals are affected by pin configuration are designated client devices. Again, each client device must be represented as a node in device tree, just like any other hardware module. For a client device to operate correctly, certain pin controllers must set up certain specific pin configurations. Some client devices need a single static pin configuration, e.g. set up during initialization. Others need to reconfigure pins at run-time, for example to tri-state pins when the device is inactive. Hence, each client device can define a set of named states. The number and names of those states is defined by the client device's own binding. The common pinctrl bindings defined in this file provide an infrastructure for client device device tree nodes to map those state names to the pin configuration used by those states. Note that pin controllers themselves may also be client devices of themselves. For example, a pin controller may set up its own "active" state when the driver loads. This would allow representing a board's static pin configuration in a single place, rather than splitting it across multiple client device nodes. The decision to do this or not somewhat rests with the author of individual board device tree files, and any requirements imposed by the bindings for the individual client devices in use by that board, i.e. whether they require certain specific named states for dynamic pin configuration. == Pinctrl client devices == For each client device individually, every pin state is assigned an integer ID. These numbers start at 0, and are contiguous. For each state ID, a unique property exists to define the pin configuration. Each state may also be assigned a name. When names are used, another property exists to map from those names to the integer IDs. Each client device's own binding determines the set of states that must be defined in its device tree node, and whether to define the set of state IDs that must be provided, or whether to define the set of state names that must be provided. Required properties: pinctrl-0: List of phandles, each pointing at a pin configuration node. These referenced pin configuration nodes must be child nodes of the pin controller that they configure. Multiple entries may exist in this list so that multiple pin controllers may be configured, or so that a state may be built from multiple nodes for a single pin controller, each contributing part of the overall configuration. See the next section of this document for details of the format of these pin configuration nodes. In some cases, it may be useful to define a state, but for it to be empty. This may be required when a common IP block is used in an SoC either without a pin controller, or where the pin controller does not affect the HW module in question. If the binding for that IP block requires certain pin states to exist, they must still be defined, but may be left empty. Optional properties: pinctrl-1: List of phandles, each pointing at a pin configuration node within a pin controller. ... pinctrl-n: List of phandles, each pointing at a pin configuration node within a pin controller. pinctrl-names: The list of names to assign states. List entry 0 defines the name for integer state ID 0, list entry 1 for state ID 1, and so on. For example: /* For a client device requiring named states */ device { pinctrl-names = "active", "idle"; pinctrl-0 = <&state_0_node_a>; pinctrl-1 = <&state_1_node_a &state_1_node_b>; }; /* For the same device if using state IDs */ device { pinctrl-0 = <&state_0_node_a>; pinctrl-1 = <&state_1_node_a &state_1_node_b>; }; /* * For an IP block whose binding supports pin configuration, * but in use on an SoC that doesn't have any pin control hardware */ device { pinctrl-names = "active", "idle"; pinctrl-0 = <>; pinctrl-1 = <>; }; == Pin controller devices == Required properties: See the pin controller driver specific documentation Optional properties: #pinctrl-cells: Number of pin control cells in addition to the index within the pin controller device instance pinctrl-use-default: Boolean. Indicates that the OS can use the boot default pin configuration. This allows using an OS that does not have a driver for the pin controller. This property can be set either globally for the pin controller or in child nodes for individual pin group control. Pin controller devices should contain the pin configuration nodes that client devices reference. For example: pincontroller { ... /* Standard DT properties for the device itself elided */ state_0_node_a { ... }; state_1_node_a { ... }; state_1_node_b { ... }; } The contents of each of those pin configuration child nodes is defined entirely by the binding for the individual pin controller device. There exists no common standard for this content. The pinctrl framework only provides generic helper bindings that the pin controller driver can use. The pin configuration nodes need not be direct children of the pin controller device; they may be grandchildren, for example. Whether this is legal, and whether there is any interaction between the child and intermediate parent nodes, is again defined entirely by the binding for the individual pin controller device. == Generic pin multiplexing node content == pin multiplexing nodes: function - the mux function to select groups - the list of groups to select with this function (either this or "pins" must be specified) pins - the list of pins to select with this function (either this or "groups" must be specified) Example: state_0_node_a { uart0 { function = "uart0"; groups = "u0rxtx", "u0rtscts"; }; }; state_1_node_a { spi0 { function = "spi0"; groups = "spi0pins"; }; }; state_2_node_a { function = "i2c0"; pins = "mfio29", "mfio30"; }; Optionally an alternative binding can be used if more suitable depending on the pin controller hardware. For hardware where there is a large number of identical pin controller instances, naming each pin and function can easily become unmaintainable. This is especially the case if the same controller is used for different pins and functions depending on the SoC revision and packaging. For cases like this, the pin controller driver may use pinctrl-pin-array helper binding with a hardware based index and a number of pin configuration values: pincontroller { ... /* Standard DT properties for the device itself elided */ #pinctrl-cells = <2>; state_0_node_a { pinctrl-pin-array = < 0 A_DELAY_PS(0) G_DELAY_PS(120) 4 A_DELAY_PS(0) G_DELAY_PS(360) ... >; }; ... }; Above #pinctrl-cells specifies the number of value cells in addition to the index of the registers. This is similar to the interrupts-extended binding with one exception. There is no need to specify the phandle for each entry as that is already known as the defined pins are always children of the pin controller node. Further having the phandle pointing to another pin controller would not currently work as the pinctrl framework uses named modes to group pins for each pin control device. The index for pinctrl-pin-array must relate to the hardware for the pinctrl registers, and must not be a virtual index of pin instances. The reason for this is to avoid mapping of the index in the dts files and the pin controller driver as it can change. For hardware where pin multiplexing configurations have to be specified for each single pin the number of required sub-nodes containing "pin" and "function" properties can quickly escalate and become hard to write and maintain. For cases like this, the pin controller driver may use the pinmux helper property, where the pin identifier is provided with mux configuration settings in a pinmux group. A pinmux group consists of the pin identifier and mux settings represented as a single integer or an array of integers. The pinmux property accepts an array of pinmux groups, each of them describing a single pin multiplexing configuration. pincontroller { state_0_node_a { pinmux = , , ...; }; }; Each individual pin controller driver bindings documentation shall specify how pin IDs and pin multiplexing configuration are defined and assembled together in a pinmux group. == Generic pin configuration node content == Many data items that are represented in a pin configuration node are common and generic. Pin control bindings should use the properties defined below where they are applicable; not all of these properties are relevant or useful for all hardware or binding structures. Each individual binding document should state which of these generic properties, if any, are used, and the structure of the DT nodes that contain these properties. Supported generic properties are: pins - the list of pins that properties in the node apply to (either this, "group" or "pinmux" has to be specified) group - the group to apply the properties to, if the driver supports configuration of whole groups rather than individual pins (either this, "pins" or "pinmux" has to be specified) pinmux - the list of numeric pin ids and their mux settings that properties in the node apply to (either this, "pins" or "groups" have to be specified) bias-disable - disable any pin bias bias-high-impedance - high impedance mode ("third-state", "floating") bias-bus-hold - latch weakly bias-pull-up - pull up the pin bias-pull-down - pull down the pin bias-pull-pin-default - use pin-default pull state drive-push-pull - drive actively high and low drive-open-drain - drive with open drain drive-open-source - drive with open source drive-strength - sink or source at most X mA drive-strength-microamp - sink or source at most X uA input-enable - enable input on pin (no effect on output, such as enabling an input buffer) input-disable - disable input on pin (no effect on output, such as disabling an input buffer) input-schmitt-enable - enable schmitt-trigger mode input-schmitt-disable - disable schmitt-trigger mode input-debounce - debounce mode with debound time X power-source - select between different power supplies low-power-enable - enable low power mode low-power-disable - disable low power mode output-disable - disable output on a pin (such as disable an output buffer) output-enable - enable output on a pin without actively driving it (such as enabling an output buffer) output-low - set the pin to output mode with low level output-high - set the pin to output mode with high level sleep-hardware-state - indicate this is sleep related state which will be programmed into the registers for the sleep state. slew-rate - set the slew rate skew-delay - this affects the expected clock skew on input pins and the delay before latching a value to an output pin. Typically indicates how many double-inverters are used to delay the signal. For example: state_0_node_a { cts_rxd { pins = "GPIO0_AJ5", "GPIO2_AH4"; /* CTS+RXD */ bias-pull-up; }; }; state_1_node_a { rts_txd { pins = "GPIO1_AJ3", "GPIO3_AH3"; /* RTS+TXD */ output-high; }; }; state_2_node_a { foo { group = "foo-group"; bias-pull-up; }; }; state_3_node_a { mux { pinmux = , ; input-enable; }; }; Some of the generic properties take arguments. For those that do, the arguments are described below. - pins takes a list of pin names or IDs as a required argument. The specific binding for the hardware defines: - Whether the entries are integers or strings, and their meaning. - pinmux takes a list of pin IDs and mux settings as required argument. The specific bindings for the hardware defines: - How pin IDs and mux settings are defined and assembled together in a single integer or an array of integers. - bias-pull-up, -down and -pin-default take as optional argument on hardware supporting it the pull strength in Ohm. bias-disable will disable the pull. - drive-strength takes as argument the target strength in mA. - drive-strength-microamp takes as argument the target strength in uA. - input-debounce takes the debounce time in usec as argument or 0 to disable debouncing More in-depth documentation on these parameters can be found in