Bug 86761

Summary:	Minimum backlight brightness too high [Notebook W65_67SZ, Intel HD Graphics 4600]
Product:	Drivers	Reporter:	vej.kse
Component:	Video(DRI - Intel)	Assignee:	intel-gfx-bugs (intel-gfx-bugs)
Status:	RESOLVED OBSOLETE
Severity:	normal	CC:	intel-gfx-bugs
Priority:	P1
Hardware:	Intel
OS:	Linux
Kernel Version:	3.17.1	Subsystem:
Regression:	Yes	Bisected commit-id:

Description vej.kse 2014-10-23 18:20:07 UTC

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.

Comment 1 Jani Nikula 2015-01-28 15:13:28 UTC

Details in
commit 6dda730e55f412a6dfb181cae6784822ba463847
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Tue Jun 24 18:27:40 2014 +0300

    drm/i915: respect the VBT minimum backlight brightness

Comment 2 Jani Nikula 2015-02-11 14:34:35 UTC

How's v3.19 kernel?

Comment 3 Jani Nikula 2015-06-16 09:43:12 UTC

Timeout.