mirror of https://gitee.com/openkylin/linux.git
97 lines
4.9 KiB
Plaintext
97 lines
4.9 KiB
Plaintext
Special Usage Model of the ACPI Control Method Lid Device
|
|
|
|
Copyright (C) 2016, Intel Corporation
|
|
Author: Lv Zheng <lv.zheng@intel.com>
|
|
|
|
|
|
Abstract:
|
|
|
|
Platforms containing lids convey lid state (open/close) to OSPMs using a
|
|
control method lid device. To implement this, the AML tables issue
|
|
Notify(lid_device, 0x80) to notify the OSPMs whenever the lid state has
|
|
changed. The _LID control method for the lid device must be implemented to
|
|
report the "current" state of the lid as either "opened" or "closed".
|
|
|
|
For most platforms, both the _LID method and the lid notifications are
|
|
reliable. However, there are exceptions. In order to work with these
|
|
exceptional buggy platforms, special restrictions and expections should be
|
|
taken into account. This document describes the restrictions and the
|
|
expections of the Linux ACPI lid device driver.
|
|
|
|
|
|
1. Restrictions of the returning value of the _LID control method
|
|
|
|
The _LID control method is described to return the "current" lid state.
|
|
However the word of "current" has ambiguity, some buggy AML tables return
|
|
the lid state upon the last lid notification instead of returning the lid
|
|
state upon the last _LID evaluation. There won't be difference when the
|
|
_LID control method is evaluated during the runtime, the problem is its
|
|
initial returning value. When the AML tables implement this control method
|
|
with cached value, the initial returning value is likely not reliable.
|
|
There are platforms always retun "closed" as initial lid state.
|
|
|
|
2. Restrictions of the lid state change notifications
|
|
|
|
There are buggy AML tables never notifying when the lid device state is
|
|
changed to "opened". Thus the "opened" notification is not guaranteed. But
|
|
it is guaranteed that the AML tables always notify "closed" when the lid
|
|
state is changed to "closed". The "closed" notification is normally used to
|
|
trigger some system power saving operations on Windows. Since it is fully
|
|
tested, it is reliable from all AML tables.
|
|
|
|
3. Expections for the userspace users of the ACPI lid device driver
|
|
|
|
The ACPI button driver exports the lid state to the userspace via the
|
|
following file:
|
|
/proc/acpi/button/lid/LID0/state
|
|
This file actually calls the _LID control method described above. And given
|
|
the previous explanation, it is not reliable enough on some platforms. So
|
|
it is advised for the userspace program to not to solely rely on this file
|
|
to determine the actual lid state.
|
|
|
|
The ACPI button driver emits the following input event to the userspace:
|
|
SW_LID
|
|
The ACPI lid device driver is implemented to try to deliver the platform
|
|
triggered events to the userspace. However, given the fact that the buggy
|
|
firmware cannot make sure "opened"/"closed" events are paired, the ACPI
|
|
button driver uses the following 3 modes in order not to trigger issues.
|
|
|
|
If the userspace hasn't been prepared to ignore the unreliable "opened"
|
|
events and the unreliable initial state notification, Linux users can use
|
|
the following kernel parameters to handle the possible issues:
|
|
A. button.lid_init_state=method:
|
|
When this option is specified, the ACPI button driver reports the
|
|
initial lid state using the returning value of the _LID control method
|
|
and whether the "opened"/"closed" events are paired fully relies on the
|
|
firmware implementation.
|
|
This option can be used to fix some platforms where the returning value
|
|
of the _LID control method is reliable but the initial lid state
|
|
notification is missing.
|
|
This option is the default behavior during the period the userspace
|
|
isn't ready to handle the buggy AML tables.
|
|
B. button.lid_init_state=open:
|
|
When this option is specified, the ACPI button driver always reports the
|
|
initial lid state as "opened" and whether the "opened"/"closed" events
|
|
are paired fully relies on the firmware implementation.
|
|
This may fix some platforms where the returning value of the _LID
|
|
control method is not reliable and the initial lid state notification is
|
|
missing.
|
|
|
|
If the userspace has been prepared to ignore the unreliable "opened" events
|
|
and the unreliable initial state notification, Linux users should always
|
|
use the following kernel parameter:
|
|
C. button.lid_init_state=ignore:
|
|
When this option is specified, the ACPI button driver never reports the
|
|
initial lid state and there is a compensation mechanism implemented to
|
|
ensure that the reliable "closed" notifications can always be delievered
|
|
to the userspace by always pairing "closed" input events with complement
|
|
"opened" input events. But there is still no guarantee that the "opened"
|
|
notifications can be delivered to the userspace when the lid is actually
|
|
opens given that some AML tables do not send "opened" notifications
|
|
reliably.
|
|
In this mode, if everything is correctly implemented by the platform
|
|
firmware, the old userspace programs should still work. Otherwise, the
|
|
new userspace programs are required to work with the ACPI button driver.
|
|
This option will be the default behavior after the userspace is ready to
|
|
handle the buggy AML tables.
|