Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt - arm/linux-arm64-legacy - Git at Google

 == 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.

 == 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
 function		- the mux function to select
 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
 input-enable		- enable input on pin (no effect on output)
 input-disable		- disable input on pin (no effect on output)
 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-low		- set the pin to output mode with low level
 output-high		- set the pin to output mode with high level
 slew-rate		- set the slew rate

 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.

 - function takes a list of function names/IDs as a required argument. The
   specific binding for the hardware defines:
   - Whether the entries are integers or strings, and their meaning.
   - Whether only a single entry is allowed (which is applied to all entries
     in the pins property), or whether there may alternatively be one entry per
     entry in the pins property, in which case the list lengths must match, and
     for each list index i, the function at list index i is applied to the pin
     at list index i.

 - 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.

 - 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
 <include/linux/pinctrl/pinconfig-generic.h>
	== 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.

	== 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
	function - the mux function to select
	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
	input-enable - enable input on pin (no effect on output)
	input-disable - disable input on pin (no effect on output)
	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-low - set the pin to output mode with low level
	output-high - set the pin to output mode with high level
	slew-rate - set the slew rate

	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.

	- function takes a list of function names/IDs as a required argument. The
	specific binding for the hardware defines:
	- Whether the entries are integers or strings, and their meaning.
	- Whether only a single entry is allowed (which is applied to all entries
	in the pins property), or whether there may alternatively be one entry per
	entry in the pins property, in which case the list lengths must match, and
	for each list index i, the function at list index i is applied to the pin
	at list index i.

	- 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.

	- 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
	<include/linux/pinctrl/pinconfig-generic.h>