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On kernel 4.10 the backlight on my skylake + optimus (nvidia gtx960m) worked
perfectly. But with kernel 4.11, in /sys/class/backlight, an acpi_video0 entry
appears instead of intel_backlight. Echoing a value into the brightness
property is accepted with kernel 4.11, but does not result into a change of
brightness.

Boot options such as acpi_osi=Linux and other options such as
video.use_native_backlight=1 do not result in fixing the problem.

On kernel 4.10, lspci -v shows the following for graphics hardware:
00:02.0 VGA compatible controller: Intel Corporation HD Graphics 530 (rev 06)
(prog-if 00 [VGA controller])
        Subsystem: CLEVO/KAPOK Computer Device 1501
        Flags: bus master, fast devsel, latency 0, IRQ 126
        Memory at dd000000 (64-bit, non-prefetchable) [size=16M]
        Memory at a0000000 (64-bit, prefetchable) [size=512M]
        I/O ports at f000 [size=64]
        [virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
        Capabilities: [40] Vendor Specific Information: Len=0c <?>
        Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
        Capabilities: [ac] MSI: Enable+ Count=1/1 Maskable- 64bit-
        Capabilities: [d0] Power Management version 2
        Capabilities: [100] Process Address Space ID (PASID)
        Capabilities: [200] Address Translation Service (ATS)
        Capabilities: [300] Page Request Interface (PRI)
        Kernel driver in use: i915
        Kernel modules: i915

01:00.0 VGA compatible controller: NVIDIA Corporation GM107M [GeForce GTX 960M]
(rev a2) (prog-if 00 [VGA controller])
        Subsystem: CLEVO/KAPOK Computer Device 1501
        Flags: bus master, fast devsel, latency 0, IRQ 16
        Memory at de000000 (32-bit, non-prefetchable) [size=16M]
        Memory at c0000000 (64-bit, prefetchable) [size=256M]
        Memory at d0000000 (64-bit, prefetchable) [size=32M]
        I/O ports at e000 [size=128]
        Expansion ROM at df000000 [disabled] [size=512K]
        Capabilities: [60] Power Management version 3
        Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
        Capabilities: [78] Express Legacy Endpoint, MSI 00
        Capabilities: [100] Virtual Channel
        Capabilities: [250] Latency Tolerance Reporting
        Capabilities: [258] L1 PM Substates
        Capabilities: [128] Power Budgeting <?>
        Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024
<?>
        Capabilities: [900] #19
        Kernel driver in use: nvidia
        Kernel modules: nouveau, nvidia_drm, nvidia


Reproducible: Always

Steps to Reproduce:
1. Just boot the system with any kernel 4.11

Actual Results:  
/sys/class/backlight/acpi_video0 appears.

Echoing a value into /sys/class/backlight/acpi_video0/brightness does not
change the brightness of the screen.

Expected Results:  
/sys/class/backlight/intel_backlight

This is what I get with kernel 4.10.13-1
Echoing a value into /sys/class/backlight/intel_backlight/brightness does
change the brightness