[Bug 86761] New: Minimum backlight brightness too high [Notebook W65_67SZ, Intel HD Graphics 4600]

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=86761

            Bug ID: 86761
           Summary: Minimum backlight brightness too high [Notebook
                    W65_67SZ, Intel HD Graphics 4600]
           Product: Drivers
           Version: 2.5
    Kernel Version: 3.17.1
          Hardware: Intel
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - Intel)
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: vej.kse at gmail.com
                CC: intel-gfx-bugs at lists.freedesktop.org
        Regression: No

Since version 3.17.1 of the kernel, the minimum backlight brightness I can get
using either the backlight keys or xbacklight is too high to be comfortable in
the evening (even with the roomlights on).  Downgrading to 3.16.4 solves the
issue.  With 3.17.1, this high brightness corresponds to a 0 value for
/sys/class/backlight/intel_backlight/actual_brightness and
/sys/class/backlight/intel_backlight/brightness , whereas with 3.16.4, the
lowest value I can get there is 8, which is way darker (but still readable in
the dark) than what 3.17.1 calls “0”.

It could be useful to mention that the backlight keys work with
“video.use_native_backlight=0”, but not with this setting set to 1, nor with
“acpi_backlight=vendor” + “acpi_osi=linux” (but I can still use xbacklight with
these settings).  Changing these options has no effect on the minimum
brightness.

I'm using ArchLinux, the packages being:
- for 3.17.1: linux 3.17.1-1, build date: 2014-10-15 13:06 UTC
- for 3.16.4: linux 3.16.4-1, build date: 2014-10-06 08:26 CEST.

My computer is a Notebook W65_67SZ, with Intel HD Graphics 4600.

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