1 .. SPDX-License-Identifier: GPL-2.0
2 .. include:: <isonum.txt>
3
4 ==============================================
5 Special Usage Model of the ACPI Control Method
6 ==============================================
7
8 :Copyright: |copy| 2016, Intel Corporation
9
10 :Author: Lv Zheng <lv.zheng@intel.com>
11
12 Abstract
13 ========
14 Platforms containing lids convey lid state (op
15 using a control method lid device. To implemen
16 Notify(lid_device, 0x80) to notify the OSPMs w
17 changed. The _LID control method for the lid d
18 report the "current" state of the lid as eithe
19
20 For most platforms, both the _LID method and t
21 reliable. However, there are exceptions. In or
22 exceptional buggy platforms, special restricti
23 taken into account. This document describes th
24 exceptions of the Linux ACPI lid device driver
25
26
27 Restrictions of the returning value of the _LI
28 ==============================================
29
30 The _LID control method is described to return
31 However the word of "current" has ambiguity, s
32 the lid state upon the last lid notification i
33 state upon the last _LID evaluation. There won
34 _LID control method is evaluated during the ru
35 initial returning value. When the AML tables i
36 with cached value, the initial returning value
37 There are platforms always return "closed" as
38
39 Restrictions of the lid state change notificat
40 ==============================================
41
42 There are buggy AML tables never notifying whe
43 changed to "opened". Thus the "opened" notific
44 it is guaranteed that the AML tables always no
45 state is changed to "closed". The "closed" not
46 trigger some system power saving operations on
47 tested, it is reliable from all AML tables.
48
49 Exceptions for the userspace users of the ACPI
50 ==============================================
51
52 The ACPI button driver exports the lid state t
53 following file::
54
55 /proc/acpi/button/lid/LID0/state
56
57 This file actually calls the _LID control meth
58 the previous explanation, it is not reliable e
59 it is advised for the userspace program to not
60 to determine the actual lid state.
61
62 The ACPI button driver emits the following inp
63 * SW_LID
64
65 The ACPI lid device driver is implemented to t
66 triggered events to the userspace. However, gi
67 firmware cannot make sure "opened"/"closed" ev
68 button driver uses the following 3 modes in or
69
70 If the userspace hasn't been prepared to ignor
71 events and the unreliable initial state notifi
72 the following kernel parameters to handle the
73
74 A. button.lid_init_state=method:
75 When this option is specified, the ACPI but
76 initial lid state using the returning value
77 and whether the "opened"/"closed" events ar
78 firmware implementation.
79
80 This option can be used to fix some platfor
81 of the _LID control method is reliable but
82 notification is missing.
83
84 This option is the default behavior during
85 isn't ready to handle the buggy AML tables.
86
87 B. button.lid_init_state=open:
88 When this option is specified, the ACPI but
89 initial lid state as "opened" and whether t
90 are paired fully relies on the firmware imp
91
92 This may fix some platforms where the retur
93 control method is not reliable and the init
94 missing.
95
96 If the userspace has been prepared to ignore t
97 and the unreliable initial state notification,
98 use the following kernel parameter:
99
100 C. button.lid_init_state=ignore:
101 When this option is specified, the ACPI but
102 initial lid state and there is a compensati
103 ensure that the reliable "closed" notificat
104 to the userspace by always pairing "closed"
105 "opened" input events. But there is still n
106 notifications can be delivered to the users
107 opens given that some AML tables do not sen
108 reliably.
109
110 In this mode, if everything is correctly im
111 firmware, the old userspace programs should
112 new userspace programs are required to work
113 This option will be the default behavior af
114 handle the buggy AML tables.
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