[Bug 100041] New: MacbookPro12,1 (early 2015): intel i915 iris 6100 with eDP : acpi_video backlight exists and is broken

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=100041

            Bug ID: 100041
           Summary: MacbookPro12,1 (early 2015): intel i915 iris 6100 with
                    eDP : acpi_video backlight exists and is broken
           Product: Drivers
           Version: 2.5
    Kernel Version: 4.0.4
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - Intel)
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: tormen at diplomail.ch
                CC: intel-gfx-bugs at lists.freedesktop.org
        Regression: No

//// THE SETUP ///////////////

On the MacbookPro12,1 (early 2015 Retina display version) with the graphics
adapter:

00:02.0 0300: 8086:162b (rev 09) (prog-if 00 [VGA controller])
        Subsystem: 106b:013f

00:02.0 VGA compatible controller: Intel Corporation Broadwell-U Integrated
Graphics (rev 09) (prog-if 00 [VGA controller])
        Subsystem: Apple Inc. Device 013f
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR- FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort-
<MAbort- >SERR- <PERR- INTx-
        Latency: 0
        Interrupt: pin A routed to IRQ 57
        Region 0: Memory at c0000000 (64-bit, non-prefetchable) [size=16M]
        Region 2: Memory at b0000000 (64-bit, prefetchable) [size=256M]
        Region 4: I/O ports at 3000 [size=64]
        Expansion ROM at <unassigned> [disabled]
        Capabilities: <access denied>
        Kernel driver in use: i915

//// THE PROBLEM ///////////////

If the kernel 4.0.4 is booted without any relevant kernel cmdline paramters:

There are:
  /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0
  and 
  /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight

The latter (intel_backlight) works and controls the brightness of the laptops
internal screen using a brightness scale from 0 to 1388 (adjustable  in steps
of 1 ;).

But the former (acpi_video0), which is used by the X brightness keys, has no
effect: It has a scale from 0-100 and changing it's values (trough echo under
/sys/ or using the XF86 brightness up/down keys, has no visible effect.



Using acpi_backlight=vendor fixes the problem in that it removes:
  /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0
and leaves only:
  /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight
to be found and used by X.


Please let me know if you need more information, debug, logfiles, etc.

Tormen.

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