1== Introduction == 2 3Hardware modules that control pin multiplexing or configuration parameters 4such as pull-up/down, tri-state, drive-strength etc are designated as pin 5controllers. Each pin controller must be represented as a node in device tree, 6just like any other hardware module. 7 8Hardware modules whose signals are affected by pin configuration are 9designated client devices. Again, each client device must be represented as a 10node in device tree, just like any other hardware module. 11 12For a client device to operate correctly, certain pin controllers must 13set up certain specific pin configurations. Some client devices need a 14single static pin configuration, e.g. set up during initialization. Others 15need to reconfigure pins at run-time, for example to tri-state pins when the 16device is inactive. Hence, each client device can define a set of named 17states. The number and names of those states is defined by the client device's 18own binding. 19 20The common pinctrl bindings defined in this file provide an infrastructure 21for client device device tree nodes to map those state names to the pin 22configuration used by those states. 23 24Note that pin controllers themselves may also be client devices of themselves. 25For example, a pin controller may set up its own "active" state when the 26driver loads. This would allow representing a board's static pin configuration 27in a single place, rather than splitting it across multiple client device 28nodes. The decision to do this or not somewhat rests with the author of 29individual board device tree files, and any requirements imposed by the 30bindings for the individual client devices in use by that board, i.e. whether 31they require certain specific named states for dynamic pin configuration. 32 33== Pinctrl client devices == 34 35For each client device individually, every pin state is assigned an integer 36ID. These numbers start at 0, and are contiguous. For each state ID, a unique 37property exists to define the pin configuration. Each state may also be 38assigned a name. When names are used, another property exists to map from 39those names to the integer IDs. 40 41Each client device's own binding determines the set of states the must be 42defined in its device tree node, and whether to define the set of state 43IDs that must be provided, or whether to define the set of state names that 44must be provided. 45 46Required properties: 47pinctrl-0: List of phandles, each pointing at a pin configuration 48 node. These referenced pin configuration nodes must be child 49 nodes of the pin controller that they configure. Multiple 50 entries may exist in this list so that multiple pin 51 controllers may be configured, or so that a state may be built 52 from multiple nodes for a single pin controller, each 53 contributing part of the overall configuration. See the next 54 section of this document for details of the format of these 55 pin configuration nodes. 56 57 In some cases, it may be useful to define a state, but for it 58 to be empty. This may be required when a common IP block is 59 used in an SoC either without a pin controller, or where the 60 pin controller does not affect the HW module in question. If 61 the binding for that IP block requires certain pin states to 62 exist, they must still be defined, but may be left empty. 63 64Optional properties: 65pinctrl-1: List of phandles, each pointing at a pin configuration 66 node within a pin controller. 67... 68pinctrl-n: List of phandles, each pointing at a pin configuration 69 node within a pin controller. 70pinctrl-names: The list of names to assign states. List entry 0 defines the 71 name for integer state ID 0, list entry 1 for state ID 1, and 72 so on. 73 74For example: 75 76 /* For a client device requiring named states */ 77 device { 78 pinctrl-names = "active", "idle"; 79 pinctrl-0 = <&state_0_node_a>; 80 pinctrl-1 = <&state_1_node_a &state_1_node_b>; 81 }; 82 83 /* For the same device if using state IDs */ 84 device { 85 pinctrl-0 = <&state_0_node_a>; 86 pinctrl-1 = <&state_1_node_a &state_1_node_b>; 87 }; 88 89 /* 90 * For an IP block whose binding supports pin configuration, 91 * but in use on an SoC that doesn't have any pin control hardware 92 */ 93 device { 94 pinctrl-names = "active", "idle"; 95 pinctrl-0 = <>; 96 pinctrl-1 = <>; 97 }; 98 99== Pin controller devices == 100 101Pin controller devices should contain the pin configuration nodes that client 102devices reference. 103 104For example: 105 106 pincontroller { 107 ... /* Standard DT properties for the device itself elided */ 108 109 state_0_node_a { 110 ... 111 }; 112 state_1_node_a { 113 ... 114 }; 115 state_1_node_b { 116 ... 117 }; 118 } 119 120The contents of each of those pin configuration child nodes is defined 121entirely by the binding for the individual pin controller device. There 122exists no common standard for this content. 123 124The pin configuration nodes need not be direct children of the pin controller 125device; they may be grandchildren, for example. Whether this is legal, and 126whether there is any interaction between the child and intermediate parent 127nodes, is again defined entirely by the binding for the individual pin 128controller device. 129 130== Using generic pinconfig options == 131 132Generic pinconfig parameters can be used by defining a separate node containing 133the applicable parameters (and optional values), like: 134 135pcfg_pull_up: pcfg_pull_up { 136 bias-pull-up; 137 drive-strength = <20>; 138}; 139 140This node should then be referenced in the appropriate pinctrl node as a phandle 141and parsed in the driver using the pinconf_generic_parse_dt_config function. 142 143Supported configuration parameters are: 144 145bias-disable - disable any pin bias 146bias-high-impedance - high impedance mode ("third-state", "floating") 147bias-bus-hold - latch weakly 148bias-pull-up - pull up the pin 149bias-pull-down - pull down the pin 150bias-pull-pin-default - use pin-default pull state 151drive-push-pull - drive actively high and low 152drive-open-drain - drive with open drain 153drive-open-source - drive with open source 154drive-strength - sink or source at most X mA 155input-schmitt-enable - enable schmitt-trigger mode 156input-schmitt-disable - disable schmitt-trigger mode 157input-debounce - debounce mode with debound time X 158low-power-enable - enable low power mode 159low-power-disable - disable low power mode 160output-low - set the pin to output mode with low level 161output-high - set the pin to output mode with high level 162 163Arguments for parameters: 164 165- bias-pull-up, -down and -pin-default take as optional argument on hardware 166 supporting it the pull strength in Ohm. bias-disable will disable the pull. 167 168- drive-strength takes as argument the target strength in mA. 169 170- input-debounce takes the debounce time in usec as argument 171 or 0 to disable debouncing 172 173All parameters not listed here, do not take an argument. 174 175More in-depth documentation on these parameters can be found in 176<include/linux/pinctrl/pinconfig-generic.h> 177