linux/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
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   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