Re: [PATCH 5/5] acpi_video: Don't handle ACPI brightness notifications by default

[Aaron Lu <aaron.lu@intel.com>]

On 08/04/2013 06:07 AM, Rafael J. Wysocki wrote:
> On Saturday, August 03, 2013 08:10:12 PM Aaron Lu wrote:
>> On 08/03/2013 07:23 PM, Rafael J. Wysocki wrote:
>>> On Saturday, August 03, 2013 05:46:02 PM Aaron Lu wrote:
>>>> On 08/03/2013 08:26 AM, Rafael J. Wysocki wrote:
>>>>> On Friday, August 02, 2013 10:52:09 PM Aaron Lu wrote:
>>>>>> On 08/02/2013 10:41 PM, Rafael J. Wysocki wrote:
>>>>>>> On Friday, August 02, 2013 01:55:47 PM Aaron Lu wrote:
>>>>>>>> On 03/08/2013 03:39 AM, Seth Forshee wrote:
>>>>>>>>> Windows 8 requires all backlight interfaces to report 101 brightness
>>>>>>>>> values, and as a result we're starting to see machines with that many
>>>>>>>>> brightness levels in _BCL. For machines which send these notifications
>>>>>>>>> when the brightness up/down keys are pressed this means a lot of key
>>>>>>>>> presses to get any kind of noticeable change in brightness.
>>>>>>>>>
>>>>>>>>> For a while now we've had the ability to disable in-kernel handling of
>>>>>>>>> notifications via the video.brightness_switch_enabled parameter. Change
>>>>>>>>> this to default to off, and let userspace choose more reasonable
>>>>>>>>> increments for changing the brightness.
>>>>>>>>
>>>>>>>> I just found one more reason for this param to default 0.
>>>>>>>
>>>>>>> Do you mean video.brightness_switch_enabled?
>>>>>>
>>>>>> Yes.
>>>>>>
>>>>>>>
>>>>>>>> We are going to separate the backlight interface control and event
>>>>>>>> notification functionalities of the ACPI video module, it is highly
>>>>>>>> possible a lot of systems will use a combination of the event
>>>>>>>> notification handler and intel_backlight interface. So it doesn't make
>>>>>>>> sense to let video module to do any adjustment on its own if user space
>>>>>>>> has chosen a different interface to use. Actually, it can cause problems
>>>>>>>> as in ASUS's case:
>>>>>>>> https://bugzilla.kernel.org/show_bug.cgi?id=52951
>>>>>>>>
>>>>>>>> The problem there is, on hotkey brightness up, the video module will
>>>>>>>> adjust the brightness level first and since its _BQC is broken, it gets
>>>>>>>> a wrong number(too low or too high or whatever) and then does the _BCM
>>>>>>>> call. The _BCM method works. Then user space picks the intel_backlight
>>>>>>>> to do the adjustment, but since the _BCM already sets a wrong value, the
>>>>>>>> user space's adjustment is affected too. The result is, user has only
>>>>>>>> two visible levels, very low and very high.
>>>>>>>>
>>>>>>>> This only occurs on -rc3, since we removed the
>>>>>>>> acpi_video_verify_backlight_support from acpi_video_switch_brightness
>>>>>>>> function.
>>>>>>>
>>>>>>> What did we do before -rc2?  Did we address that in any way?
>>>>>>
>>>>>> No, before rc2, backlight is broken on that system.
>>>>>
>>>>> Well, it will have to stay that way in 3.11 I'm afraid, unless we have a fix
>>>>> or a workaround that is *guaranteed* not to introduce any new issues on any
>>>>> systems.
>>>>>
>>>>>> In rc2, we added the win8 patch and a fix patch for the hotkey, then
>>>>>> the ACPI video module's backlight control and in kernel brightness
>>>>>> handling is disabled. With the working hotkey and intel_backlight, rc2
>>>>>> works for the system. Then with the revert in rc3, user needs to choose
>>>>>> intel_backlight in xorg.conf but the in kernel brightness handling from
>>>>>> ACPI video module is back. Since video module is broken, it breaks the
>>>>>> backlight hotkey functionality.
>>>>>
>>>>> I guess we need to revert the hotkey fix too (that is efaa14c, right?)
>>>>> then, is that correct?  And try to do something smarter for 3.12?
>>>>
>>>> With or without commit efaa14c, hotkey for backlight is broken out of
>>>> box for the affected systems(ASUS N56VZ and N56VJ). But with that commit,
>>>> user has a chance of getting a working backlight with hotkey by specifying
>>>> intel_backlight and adding the video.brightness_switch_enabled=0. So I
>>>> think we can keep that commit.
>>>
>>> What about the "boot to black screen" problem, then?
>>
>> You mean this one?
>> https://lkml.org/lkml/2013/7/30/814
> 
> Yes. :-)

That is due to the broken _BQC provided by firmware, not that commit.
After we enhance the quirk for _BQC, the problem will be gone.

-Aaron