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== Generic pin configuration node content == 131 132Many data items that are represented in a pin configuration node are common 133and generic. Pin control bindings should use the properties defined below 134where they are applicable; not all of these properties are relevant or useful 135for all hardware or binding structures. Each individual binding document 136should state which of these generic properties, if any, are used, and the 137structure of the DT nodes that contain these properties. 138 139Supported generic properties are: 140 141pins - the list of pins that properties in the node 142 apply to 143function - the mux function to select 144bias-disable - disable any pin bias 145bias-high-impedance - high impedance mode ("third-state", "floating") 146bias-bus-hold - latch weakly 147bias-pull-up - pull up the pin 148bias-pull-down - pull down the pin 149bias-pull-pin-default - use pin-default pull state 150drive-push-pull - drive actively high and low 151drive-open-drain - drive with open drain 152drive-open-source - drive with open source 153drive-strength - sink or source at most X mA 154input-schmitt-enable - enable schmitt-trigger mode 155input-schmitt-disable - disable schmitt-trigger mode 156input-debounce - debounce mode with debound time X 157low-power-enable - enable low power mode 158low-power-disable - disable low power mode 159output-low - set the pin to output mode with low level 160output-high - set the pin to output mode with high level 161 162Some of the generic properties take arguments. For those that do, the 163arguments are described below. 164 165- pins takes a list of pin names or IDs as a required argument. The specific 166 binding for the hardware defines: 167 - Whether the entries are integers or strings, and their meaning. 168 169- function takes a list of function names/IDs as a required argument. The 170 specific binding for the hardware defines: 171 - Whether the entries are integers or strings, and their meaning. 172 - Whether only a single entry is allowed (which is applied to all entries 173 in the pins property), or whether there may alternatively be one entry per 174 entry in the pins property, in which case the list lengths must match, and 175 for each list index i, the function at list index i is applied to the pin 176 at list index i. 177 178- bias-pull-up, -down and -pin-default take as optional argument on hardware 179 supporting it the pull strength in Ohm. bias-disable will disable the pull. 180 181- drive-strength takes as argument the target strength in mA. 182 183- input-debounce takes the debounce time in usec as argument 184 or 0 to disable debouncing 185 186More in-depth documentation on these parameters can be found in 187<include/linux/pinctrl/pinconfig-generic.h> 188