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

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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?

Rafael

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