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Simon Glass9f4cd022015-01-05 20:05:23 -07001Specifying GPIO information for devices
2============================================
3
41) gpios property
5-----------------
6
7Nodes that makes use of GPIOs should specify them using one or more
8properties, each containing a 'gpio-list':
9
10 gpio-list ::= <single-gpio> [gpio-list]
11 single-gpio ::= <gpio-phandle> <gpio-specifier>
12 gpio-phandle : phandle to gpio controller node
13 gpio-specifier : Array of #gpio-cells specifying specific gpio
14 (controller specific)
15
16GPIO properties should be named "[<name>-]gpios", with <name> being the purpose
17of this GPIO for the device. While a non-existent <name> is considered valid
18for compatibility reasons (resolving to the "gpios" property), it is not allowed
19for new bindings.
20
21GPIO properties can contain one or more GPIO phandles, but only in exceptional
22cases should they contain more than one. If your device uses several GPIOs with
23distinct functions, reference each of them under its own property, giving it a
24meaningful name. The only case where an array of GPIOs is accepted is when
25several GPIOs serve the same function (e.g. a parallel data line).
26
27The exact purpose of each gpios property must be documented in the device tree
28binding of the device.
29
30The following example could be used to describe GPIO pins used as device enable
31and bit-banged data signals:
32
33 gpio1: gpio1 {
34 gpio-controller
35 #gpio-cells = <2>;
36 };
37 gpio2: gpio2 {
38 gpio-controller
39 #gpio-cells = <1>;
40 };
41 [...]
42
43 enable-gpios = <&gpio2 2>;
44 data-gpios = <&gpio1 12 0>,
45 <&gpio1 13 0>,
46 <&gpio1 14 0>,
47 <&gpio1 15 0>;
48
49Note that gpio-specifier length is controller dependent. In the
50above example, &gpio1 uses 2 cells to specify a gpio, while &gpio2
51only uses one.
52
53gpio-specifier may encode: bank, pin position inside the bank,
54whether pin is open-drain and whether pin is logically inverted.
55Exact meaning of each specifier cell is controller specific, and must
56be documented in the device tree binding for the device. Use the macros
57defined in include/dt-bindings/gpio/gpio.h whenever possible:
58
59Example of a node using GPIOs:
60
61 node {
62 enable-gpios = <&qe_pio_e 18 GPIO_ACTIVE_HIGH>;
63 };
64
65GPIO_ACTIVE_HIGH is 0, so in this example gpio-specifier is "18 0" and encodes
66GPIO pin number, and GPIO flags as accepted by the "qe_pio_e" gpio-controller.
67
681.1) GPIO specifier best practices
69----------------------------------
70
71A gpio-specifier should contain a flag indicating the GPIO polarity; active-
Masahiro Yamadaba257792015-02-12 18:49:33 +090072high or active-low. If it does, the following best practices should be
73followed:
Simon Glass9f4cd022015-01-05 20:05:23 -070074
75The gpio-specifier's polarity flag should represent the physical level at the
76GPIO controller that achieves (or represents, for inputs) a logically asserted
77value at the device. The exact definition of logically asserted should be
78defined by the binding for the device. If the board inverts the signal between
79the GPIO controller and the device, then the gpio-specifier will represent the
80opposite physical level than the signal at the device's pin.
81
82When the device's signal polarity is configurable, the binding for the
83device must either:
84
85a) Define a single static polarity for the signal, with the expectation that
86any software using that binding would statically program the device to use
87that signal polarity.
88
89The static choice of polarity may be either:
90
91a1) (Preferred) Dictated by a binding-specific DT property.
92
93or:
94
95a2) Defined statically by the DT binding itself.
96
97In particular, the polarity cannot be derived from the gpio-specifier, since
98that would prevent the DT from separately representing the two orthogonal
99concepts of configurable signal polarity in the device, and possible board-
100level signal inversion.
101
102or:
103
104b) Pick a single option for device signal polarity, and document this choice
105in the binding. The gpio-specifier should represent the polarity of the signal
106(at the GPIO controller) assuming that the device is configured for this
107particular signal polarity choice. If software chooses to program the device
108to generate or receive a signal of the opposite polarity, software will be
109responsible for correctly interpreting (inverting) the GPIO signal at the GPIO
110controller.
111
1122) gpio-controller nodes
113------------------------
114
115Every GPIO controller node must contain both an empty "gpio-controller"
116property, and a #gpio-cells integer property, which indicates the number of
117cells in a gpio-specifier.
118
119Example of two SOC GPIO banks defined as gpio-controller nodes:
120
121 qe_pio_a: gpio-controller@1400 {
122 compatible = "fsl,qe-pario-bank-a", "fsl,qe-pario-bank";
123 reg = <0x1400 0x18>;
124 gpio-controller;
125 #gpio-cells = <2>;
126 };
127
128 qe_pio_e: gpio-controller@1460 {
129 compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank";
130 reg = <0x1460 0x18>;
131 gpio-controller;
132 #gpio-cells = <2>;
133 };
134
1352.1) gpio- and pin-controller interaction
136-----------------------------------------
137
138Some or all of the GPIOs provided by a GPIO controller may be routed to pins
139on the package via a pin controller. This allows muxing those pins between
140GPIO and other functions.
141
142It is useful to represent which GPIOs correspond to which pins on which pin
143controllers. The gpio-ranges property described below represents this, and
144contains information structures as follows:
145
146 gpio-range-list ::= <single-gpio-range> [gpio-range-list]
147 single-gpio-range ::= <numeric-gpio-range> | <named-gpio-range>
148 numeric-gpio-range ::=
149 <pinctrl-phandle> <gpio-base> <pinctrl-base> <count>
150 named-gpio-range ::= <pinctrl-phandle> <gpio-base> '<0 0>'
Masahiro Yamadaba257792015-02-12 18:49:33 +0900151 pinctrl-phandle : phandle to pin controller node
Simon Glass9f4cd022015-01-05 20:05:23 -0700152 gpio-base : Base GPIO ID in the GPIO controller
153 pinctrl-base : Base pinctrl pin ID in the pin controller
154 count : The number of GPIOs/pins in this range
155
156The "pin controller node" mentioned above must conform to the bindings
157described in ../pinctrl/pinctrl-bindings.txt.
158
159In case named gpio ranges are used (ranges with both <pinctrl-base> and
160<count> set to 0), the property gpio-ranges-group-names contains one string
161for every single-gpio-range in gpio-ranges:
162 gpiorange-names-list ::= <gpiorange-name> [gpiorange-names-list]
163 gpiorange-name : Name of the pingroup associated to the GPIO range in
164 the respective pin controller.
165
166Elements of gpiorange-names-list corresponding to numeric ranges contain
167the empty string. Elements of gpiorange-names-list corresponding to named
168ranges contain the name of a pin group defined in the respective pin
169controller. The number of pins/GPIOs in the range is the number of pins in
170that pin group.
171
172Previous versions of this binding required all pin controller nodes that
173were referenced by any gpio-ranges property to contain a property named
174#gpio-range-cells with value <3>. This requirement is now deprecated.
175However, that property may still exist in older device trees for
176compatibility reasons, and would still be required even in new device
177trees that need to be compatible with older software.
178
179Example 1:
180
181 qe_pio_e: gpio-controller@1460 {
182 #gpio-cells = <2>;
183 compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank";
184 reg = <0x1460 0x18>;
185 gpio-controller;
186 gpio-ranges = <&pinctrl1 0 20 10>, <&pinctrl2 10 50 20>;
187 };
188
189Here, a single GPIO controller has GPIOs 0..9 routed to pin controller
190pinctrl1's pins 20..29, and GPIOs 10..19 routed to pin controller pinctrl2's
191pins 50..59.
192
193Example 2:
194
195 gpio_pio_i: gpio-controller@14B0 {
196 #gpio-cells = <2>;
197 compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank";
198 reg = <0x1480 0x18>;
199 gpio-controller;
200 gpio-ranges = <&pinctrl1 0 20 10>,
201 <&pinctrl2 10 0 0>,
202 <&pinctrl1 15 0 10>,
203 <&pinctrl2 25 0 0>;
204 gpio-ranges-group-names = "",
205 "foo",
206 "",
207 "bar";
208 };
209
210Here, three GPIO ranges are defined wrt. two pin controllers. pinctrl1 GPIO
211ranges are defined using pin numbers whereas the GPIO ranges wrt. pinctrl2
212are named "foo" and "bar".