1 .. SPDX-License-Identifier: GPL-2.0-or-later
2
3 Configfs GPIO Simulator
4 =======================
5
6 The configfs GPIO Simulator (gpio-sim) provide
7 chips for testing purposes. The lines exposed
8 using the standard GPIO character device inter
9 using sysfs attributes.
10
11 Creating simulated chips
12 ------------------------
13
14 The gpio-sim module registers a configfs subsy
15 details of the configfs filesystem, please ref
16
17 The user can create a hierarchy of configfs gr
18 values of exposed attributes. Once the chip is
19 will be translated to appropriate device prope
20
21 **Group:** ``/config/gpio-sim``
22
23 This is the top directory of the gpio-sim conf
24
25 **Group:** ``/config/gpio-sim/gpio-device``
26
27 **Attribute:** ``/config/gpio-sim/gpio-device/
28
29 **Attribute:** ``/config/gpio-sim/gpio-device/
30
31 This is a directory representing a GPIO platfo
32 attribute is read-only and allows the user-spa
33 name (e.g. ``'gpio-sim.0'``). The ``'live'`` a
34 actual creation of the device once it's fully
35 are: ``'1'`` to enable the simulated device an
36 it down.
37
38 **Group:** ``/config/gpio-sim/gpio-device/gpio
39
40 **Attribute:** ``/config/gpio-sim/gpio-device/
41
42 **Attribute:** ``/config/gpio-sim/gpio-device/
43
44 This group represents a bank of GPIOs under th
45 ``'chip_name'`` attribute is read-only and all
46 device name of the bank device. The ``'num_lin
47 the number of lines exposed by this bank.
48
49 **Group:** ``/config/gpio-sim/gpio-device/gpio
50
51 **Attribute:** ``/config/gpio-sim/gpio-device/
52
53 This group represents a single line at the off
54 allows to set the line name as represented by
55
56 **Item:** ``/config/gpio-sim/gpio-device/gpio-
57
58 **Attribute:** ``/config/gpio-sim/gpio-device/
59
60 **Attribute:** ``/config/gpio-sim/gpio-device/
61
62 This item makes the gpio-sim module hog the as
63 attribute specifies the in-kernel consumer nam
64 attribute specifies the hog direction and must
65 ``'output-high'`` and ``'output-low'``.
66
67 Inside each bank directory, there's a set of a
68 configure the new chip. Additionally the user
69 inside the chip's directory that allow to pass
70 specific lines. The name of those subdirectori
71 ``'line<offset>'`` (e.g. ``'line0'``, ``'line2
72 used by the module to assign the config to the
73
74 Once the confiuration is complete, the ``'live
75 order to instantiate the chip. It can be set b
76 chip. The module will synchronously wait for t
77 successfully probed and if this doesn't happen
78 result in an error.
79
80 Simulated GPIO chips can also be defined in de
81 must be: ``"gpio-simulator"``. Supported prope
82
83 ``"gpio-sim,label"`` - chip label
84
85 Other standard GPIO properties (like ``"gpio-l
86 ``"gpio-hog"``) are also supported. Please ref
87 details.
88
89 An example device-tree code defining a GPIO si
90
91 .. code-block :: none
92
93 gpio-sim {
94 compatible = "gpio-simulator";
95
96 bank0 {
97 gpio-controller;
98 #gpio-cells = <2>;
99 ngpios = <16>;
100 gpio-sim,label = "dt-bank0";
101 gpio-line-names = "", "sim-foo", "
102 };
103
104 bank1 {
105 gpio-controller;
106 #gpio-cells = <2>;
107 ngpios = <8>;
108 gpio-sim,label = "dt-bank1";
109
110 line3 {
111 gpio-hog;
112 gpios = <3 0>;
113 output-high;
114 line-name = "sim-hog-from-dt";
115 };
116 };
117 };
118
119 Manipulating simulated lines
120 ----------------------------
121
122 Each simulated GPIO chip creates a separate sy
123 directory for each exposed line
124 (e.g. ``/sys/devices/platform/gpio-sim.X/gpioc
125 is of the form: ``'sim_gpioX'`` where X is the
126 group there are two attributes:
127
128 ``pull`` - allows to read and set the curr
129 every line, when writing the va
130 ``'pull-down'``
131
132 ``value`` - allows to read the current val
133 different from the pull if the
134 user-space
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