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diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt new file mode 100644 index 0000000..c95ea82 --- /dev/null +++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt @@ -0,0 +1,128 @@ +== 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 the 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 == + +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 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. |