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