This patch adds documentation for the usage model of the control method lid device. Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx> Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> Cc: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxx> Cc: Bastien Nocera: <hadess@xxxxxxxxxx> Cc: linux-input@xxxxxxxxxxxxxxx --- Documentation/acpi/acpi-lid.txt | 89 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) create mode 100644 Documentation/acpi/acpi-lid.txt diff --git a/Documentation/acpi/acpi-lid.txt b/Documentation/acpi/acpi-lid.txt new file mode 100644 index 0000000..2addedc --- /dev/null +++ b/Documentation/acpi/acpi-lid.txt @@ -0,0 +1,89 @@ +Usage Model of the ACPI Control Method Lid Device + +Copyright (C) 2016, Intel Corporation +Author: Lv Zheng <lv.zheng@xxxxxxxxx> + + +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". + +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, many 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 +simply so many examples always retuning "closed" as initial lid state. + +2. Restrictions of the lid state change notifications + +There are many 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, the "closed" notification is reliable for 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 2 kinds of events to the user space: + SW_LID + When the lid state/event is reliable, the userspace can behave + according to this input switch event. + This is a mode prepared for backward compatiblity. + KEY_EVENT_OPEN/KEY_EVENT_CLOSE + When the lid state/event is not reliable, the userspace should behave + according to these 2 input key events. + New userspace programs may only be prepared for the input key events. + +If the userspace hasn't been prepared to handle the new input lid key +events, Linux users can use the following kernel parameters to handle the +possible issues triggered because of the unreliable lid state/event: +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. + This option can be used to fix some platforms where the _LID control + method's returning value 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 new usage model. +B. button.lid_init_state=open: + When this option is specified, the ACPI button driver always reports the + initial lid state as "opened". + 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 handle the new input lid key events, +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. However, the platform may automatically report a + correct initial lid state and there is no "open" event missing. When + this is the case (everything is correctly implemented by the platform + firmware), the old input switch event based userspace can still work. + Otherwise, the userspace programs may only work based on the input key + events. + This option will be the default behavior after the userspace is ready to + handle the new usage model. -- 1.7.10 -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
