1 .. SPDX-License-Identifier: GPL-2.0-only 1 .. SPDX-License-Identifier: GPL-2.0-only
2 2
3 GPIO Testing Driver 3 GPIO Testing Driver
4 =================== 4 ===================
5 5
6 .. note:: 6 .. note::
7 7
8 This module has been obsoleted by the more 8 This module has been obsoleted by the more flexible gpio-sim.rst.
9 New developments should use that API and ex 9 New developments should use that API and existing developments are
10 encouraged to migrate as soon as possible. 10 encouraged to migrate as soon as possible.
11 This module will continue to be maintained 11 This module will continue to be maintained but no new features will be
12 added. 12 added.
13 13
14 The GPIO Testing Driver (gpio-mockup) provides 14 The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO
15 chips for testing purposes. The lines exposed 15 chips for testing purposes. The lines exposed by these chips can be accessed
16 using the standard GPIO character device inter 16 using the standard GPIO character device interface as well as manipulated
17 using the dedicated debugfs directory structur 17 using the dedicated debugfs directory structure.
18 18
19 Creating simulated chips using module params 19 Creating simulated chips using module params
20 -------------------------------------------- 20 --------------------------------------------
21 21
22 When loading the gpio-mockup driver a number o 22 When loading the gpio-mockup driver a number of parameters can be passed to the
23 module. 23 module.
24 24
25 gpio_mockup_ranges 25 gpio_mockup_ranges
26 26
27 This parameter takes an argument in th 27 This parameter takes an argument in the form of an array of integer
28 pairs. Each pair defines the base GPIO 28 pairs. Each pair defines the base GPIO number (non-negative integer)
29 and the first number after the last of 29 and the first number after the last of this chip. If the base GPIO
30 is -1, the gpiolib will assign it auto 30 is -1, the gpiolib will assign it automatically. while the following
31 parameter is the number of lines expos 31 parameter is the number of lines exposed by the chip.
32 32
33 Example: gpio_mockup_ranges=-1,8,-1,16 33 Example: gpio_mockup_ranges=-1,8,-1,16,405,409
34 34
35 The line above creates three chips. Th 35 The line above creates three chips. The first one will expose 8 lines,
36 the second 16 and the third 4. The bas 36 the second 16 and the third 4. The base GPIO for the third chip is set
37 to 405 while for two first chips it wi 37 to 405 while for two first chips it will be assigned automatically.
38 38
39 gpio_mockup_named_lines 39 gpio_mockup_named_lines
40 40
41 This parameter doesn't take any argume 41 This parameter doesn't take any arguments. It lets the driver know that
42 GPIO lines exposed by it should be nam 42 GPIO lines exposed by it should be named.
43 43
44 The name format is: gpio-mockup-X-Y wh 44 The name format is: gpio-mockup-X-Y where X is mockup chip's ID
45 and Y is the line offset. 45 and Y is the line offset.
46 46
47 Manipulating simulated lines 47 Manipulating simulated lines
48 ---------------------------- 48 ----------------------------
49 49
50 Each mockup chip creates its own subdirectory 50 Each mockup chip creates its own subdirectory in /sys/kernel/debug/gpio-mockup/.
51 The directory is named after the chip's label. 51 The directory is named after the chip's label. A symlink is also created, named
52 after the chip's name, which points to the lab 52 after the chip's name, which points to the label directory.
53 53
54 Inside each subdirectory, there's a separate a 54 Inside each subdirectory, there's a separate attribute for each GPIO line. The
55 name of the attribute represents the line's of 55 name of the attribute represents the line's offset in the chip.
56 56
57 Reading from a line attribute returns the curr 57 Reading from a line attribute returns the current value. Writing to it (0 or 1)
58 changes the configuration of the simulated pul 58 changes the configuration of the simulated pull-up/pull-down resistor
59 (1 - pull-up, 0 - pull-down). 59 (1 - pull-up, 0 - pull-down).
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