1 .. SPDX-License-Identifier: GPL-2.0
2
3 .. _GPIO_GET_LINEHANDLE_IOCTL:
4
5 *************************
6 GPIO_GET_LINEHANDLE_IOCTL
7 *************************
8
9 .. warning::
10 This ioctl is part of chardev_v1.rst and i
11 gpio-v2-get-line-ioctl.rst.
12
13 Name
14 ====
15
16 GPIO_GET_LINEHANDLE_IOCTL - Request a line or
17
18 Synopsis
19 ========
20
21 .. c:macro:: GPIO_GET_LINEHANDLE_IOCTL
22
23 ``int ioctl(int chip_fd, GPIO_GET_LINEHANDLE_I
24
25 Arguments
26 =========
27
28 ``chip_fd``
29 The file descriptor of the GPIO character
30
31 ``request``
32 The :c:type:`handle_request<gpiohandle_req
33 request and their configuration.
34
35 Description
36 ===========
37
38 Request a line or lines from the kernel.
39
40 While multiple lines may be requested, the sam
41 lines in the request.
42
43 On success, the requesting process is granted
44 value and write access to the line configurati
45
46 The state of a line, including the value of ou
47 remain as requested until the returned file de
48 file descriptor is closed, the state of the li
49 the userspace perspective, and may revert to i
50
51 Requesting a line already in use is an error (
52
53 Closing the ``chip_fd`` has no effect on exist
54
55 .. _gpio-get-linehandle-config-rules:
56
57 Configuration Rules
58 -------------------
59
60 The following configuration rules apply:
61
62 The direction flags, ``GPIOHANDLE_REQUEST_INPU
63 ``GPIOHANDLE_REQUEST_OUTPUT``, cannot be combi
64 only other flag that may be set is ``GPIOHANDL
65 line is requested "as-is" to allow reading of
66 the electrical configuration.
67
68 The drive flags, ``GPIOHANDLE_REQUEST_OPEN_xxx
69 ``GPIOHANDLE_REQUEST_OUTPUT`` to be set.
70 Only one drive flag may be set.
71 If none are set then the line is assumed push-
72
73 Only one bias flag, ``GPIOHANDLE_REQUEST_BIAS_
74 it requires a direction flag to also be set.
75 If no bias flags are set then the bias configu
76
77 Requesting an invalid configuration is an erro
78
79
80 .. _gpio-get-linehandle-config-support:
81
82 Configuration Support
83 ---------------------
84
85 Where the requested configuration is not direc
86 hardware and driver, the kernel applies one of
87
88 - reject the request
89 - emulate the feature in software
90 - treat the feature as best effort
91
92 The approach applied depends on whether the fe
93 in software, and the impact on the hardware an
94 supported.
95 The approach applied for each feature is as fo
96
97 ============== ===========
98 Feature Approach
99 ============== ===========
100 Bias best effort
101 Direction reject
102 Drive emulate
103 ============== ===========
104
105 Bias is treated as best effort to allow usersp
106 configuration for platforms that support inter
107 external bias.
108 Worst case the line floats rather than being b
109
110 Drive is emulated by switching the line to an
111 be driven.
112
113 In all cases, the configuration reported by gp
114 is the requested configuration, not the result
115 Userspace cannot determine if a feature is sup
116 emulated, or is best effort.
117
118 Return Value
119 ============
120
121 On success 0 and the :c:type:`request.fd<gpioh
122 file descriptor for the request.
123
124 On error -1 and the ``errno`` variable is set
125 Common error codes are described in error-code
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