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

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

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

-Aaron