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1 Special Usage Model of the ACPI Control Method Lid Device
10 control method lid device. To implement this, the AML tables issue
11 Notify(lid_device, 0x80) to notify the OSPMs whenever the lid state has
12 changed. The _LID control method for the lid device must be implemented to
13 report the "current" state of the lid as either "opened" or "closed".
15 For most platforms, both the _LID method and the lid notifications are
18 taken into account. This document describes the restrictions and the
19 expections of the Linux ACPI lid device driver.
22 1. Restrictions of the returning value of the _LID control method
24 The _LID control method is described to return the "current" lid state.
25 However the word of "current" has ambiguity, some buggy AML tables return
26 the lid state upon the last lid notification instead of returning the lid
27 state upon the last _LID evaluation. There won't be difference when the
28 _LID control method is evaluated during the runtime, the problem is its
29 initial returning value. When the AML tables implement this control method
30 with cached value, the initial returning value is likely not reliable.
33 2. Restrictions of the lid state change notifications
35 There are buggy AML tables never notifying when the lid device state is
36 changed to "opened". Thus the "opened" notification is not guaranteed. But
37 it is guaranteed that the AML tables always notify "closed" when the lid
42 3. Expections for the userspace users of the ACPI lid device driver
44 The ACPI button driver exports the lid state to the userspace via the
47 This file actually calls the _LID control method described above. And given
48 the previous explanation, it is not reliable enough on some platforms. So
49 it is advised for the userspace program to not to solely rely on this file
50 to determine the actual lid state.
52 The ACPI button driver emits the following input event to the userspace:
54 The ACPI lid device driver is implemented to try to deliver the platform
55 triggered events to the userspace. However, given the fact that the buggy
56 firmware cannot make sure "opened"/"closed" events are paired, the ACPI
57 button driver uses the following 3 modes in order not to trigger issues.
59 If the userspace hasn't been prepared to ignore the unreliable "opened"
60 events and the unreliable initial state notification, Linux users can use
61 the following kernel parameters to handle the possible issues:
63 When this option is specified, the ACPI button driver reports the
64 initial lid state using the returning value of the _LID control method
65 and whether the "opened"/"closed" events are paired fully relies on the
67 This option can be used to fix some platforms where the returning value
68 of the _LID control method is reliable but the initial lid state
70 This option is the default behavior during the period the userspace
71 isn't ready to handle the buggy AML tables.
73 When this option is specified, the ACPI button driver always reports the
74 initial lid state as "opened" and whether the "opened"/"closed" events
75 are paired fully relies on the firmware implementation.
76 This may fix some platforms where the returning value of the _LID
77 control method is not reliable and the initial lid state notification is
80 If the userspace has been prepared to ignore the unreliable "opened" events
81 and the unreliable initial state notification, Linux users should always
82 use the following kernel parameter:
84 When this option is specified, the ACPI button driver never reports the
86 ensure that the reliable "closed" notifications can always be delievered
87 to the userspace by always pairing "closed" input events with complement
88 "opened" input events. But there is still no guarantee that the "opened"
89 notifications can be delivered to the userspace when the lid is actually
92 In this mode, if everything is correctly implemented by the platform
93 firmware, the old userspace programs should still work. Otherwise, the
94 new userspace programs are required to work with the ACPI button driver.
95 This option will be the default behavior after the userspace is ready to
96 handle the buggy AML tables.