1 .. SPDX-License-Identifier: GPL-2.0
2
3 .. _GPIO_V2_GET_LINE_IOCTL:
4
5 **********************
6 GPIO_V2_GET_LINE_IOCTL
7 **********************
8
9 Name
10 ====
11
12 GPIO_V2_GET_LINE_IOCTL - Request a line or lin
13
14 Synopsis
15 ========
16
17 .. c:macro:: GPIO_V2_GET_LINE_IOCTL
18
19 ``int ioctl(int chip_fd, GPIO_V2_GET_LINE_IOCT
20
21 Arguments
22 =========
23
24 ``chip_fd``
25 The file descriptor of the GPIO character
26
27 ``request``
28 The :c:type:`line_request<gpio_v2_line_req
29 to request and their configuration.
30
31 Description
32 ===========
33
34 On success, the requesting process is granted
35 value, write access to the line configuration,
36 edges are detected on the line, all of which a
37 :ref:`gpio-v2-line-request`.
38
39 A number of lines may be requested in the one
40 operations are performed on the requested line
41 as possible. e.g. gpio-v2-line-get-values-ioct
42 requested lines at once.
43
44 The state of a line, including the value of ou
45 remain as requested until the returned file de
46 file descriptor is closed, the state of the li
47 the userspace perspective, and may revert to i
48
49 Requesting a line already in use is an error (
50
51 Closing the ``chip_fd`` has no effect on exist
52
53 .. _gpio-v2-get-line-config-rules:
54
55 Configuration Rules
56 -------------------
57
58 For any given requested line, the following co
59
60 The direction flags, ``GPIO_V2_LINE_FLAG_INPUT
61 ``GPIO_V2_LINE_FLAG_OUTPUT``, cannot be combin
62 the only other flag that may be set is ``GPIO_
63 and the line is requested "as-is" to allow rea
64 without altering the electrical configuration.
65
66 The drive flags, ``GPIO_V2_LINE_FLAG_OPEN_xxx`
67 ``GPIO_V2_LINE_FLAG_OUTPUT`` to be set.
68 Only one drive flag may be set.
69 If none are set then the line is assumed push-
70
71 Only one bias flag, ``GPIO_V2_LINE_FLAG_BIAS_x
72 requires a direction flag to also be set.
73 If no bias flags are set then the bias configu
74
75 The edge flags, ``GPIO_V2_LINE_FLAG_EDGE_xxx``
76 ``GPIO_V2_LINE_FLAG_INPUT`` to be set and may
77 and falling edges. Requesting edge detection
78 it is an error (**ENXIO**).
79
80 Only one event clock flag, ``GPIO_V2_LINE_FLAG
81 If none are set then the event clock defaults
82 The ``GPIO_V2_LINE_FLAG_EVENT_CLOCK_HTE`` flag
83 and a kernel with ``CONFIG_HTE`` set. Request
84 doesn't support it is an error (**EOPNOTSUPP**
85
86 The :c:type:`debounce_period_us<gpio_v2_line_a
87 be applied to lines with ``GPIO_V2_LINE_FLAG_I
88 applies to both the values returned by gpio-v2
89 the edges returned by gpio-v2-line-event-read.
90 supported directly by hardware, debouncing is
91 kernel. Requesting debounce on a line that su
92 hardware nor interrupts, as required for softw
93 (**ENXIO**).
94
95 Requesting an invalid configuration is an erro
96
97 .. _gpio-v2-get-line-config-support:
98
99 Configuration Support
100 ---------------------
101
102 Where the requested configuration is not direc
103 hardware and driver, the kernel applies one of
104
105 - reject the request
106 - emulate the feature in software
107 - treat the feature as best effort
108
109 The approach applied depends on whether the fe
110 in software, and the impact on the hardware an
111 supported.
112 The approach applied for each feature is as fo
113
114 ============== ===========
115 Feature Approach
116 ============== ===========
117 Bias best effort
118 Debounce emulate
119 Direction reject
120 Drive emulate
121 Edge Detection reject
122 ============== ===========
123
124 Bias is treated as best effort to allow usersp
125 configuration for platforms that support inter
126 external bias.
127 Worst case the line floats rather than being b
128
129 Debounce is emulated by applying a filter to h
130 An edge event is generated after an edge is de
131 stable for the debounce period.
132 The event timestamp corresponds to the end of
133
134 Drive is emulated by switching the line to an
135 be actively driven.
136
137 Edge detection requires interrupt support, and
138 supported. Emulation by polling can still be p
139
140 In all cases, the configuration reported by gp
141 is the requested configuration, not the result
142 Userspace cannot determine if a feature is sup
143 emulated, or is best effort.
144
145 Return Value
146 ============
147
148 On success 0 and the :c:type:`request.fd<gpio_
149 file descriptor for the request.
150
151 On error -1 and the ``errno`` variable is set
152 Common error codes are described in error-code
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