Bug 67031

Summary:	Lenovo L530: the brightness is updated only for certain values multiple of 5 (max = 100)
Product:	ACPI	Reporter:	Sébastien Wilmet (sebastien.wilmet)
Component:	Power-Video	Assignee:	Aaron Lu (aaron.lu)
Status:	CLOSED DUPLICATE
Severity:	normal	CC:	aaron.lu, lenb
Priority:	P1
Hardware:	x86-64
OS:	Linux
Kernel Version:	3.11.10	Subsystem:
Regression:	No	Bisected commit-id:
Attachments:	Output of acpidump Output of dmidecode

Description Sébastien Wilmet 2013-12-15 21:55:24 UTC

With my Lenovo L530, the brightness doesn't work well. When I press Fn + F8 or F9 to modify the screen brightness, xfce4-power-manager (or another component) modifies /sys/class/backlight/acpi_video0/brightness, but the brightness changes only for certain values multiple of 5.

# pwd
/sys/class/backlight/acpi_video0
# cat max_brightness 
100
# cat brightness
100
# echo 89 > brightness
It doesn't work. If the brightness is at 100 and I press Fn + F8, the value is 89, and the screen brightness doesn't change.
# echo 80
Now it works. Most multiples of 5 work, but not all. For example 95 doesn't work.

I use Debian testing (up-to-date), with Linux version 3.11.10, and Xfce 4.10.

I think it is a regression in the kernel.

Comment 1 Aaron Lu 2013-12-17 07:33:25 UTC

With Linus' kernel tree v3.13-rcX, please test adding video.use_native_backlight=1 to kernel cmdline and report back, thanks.

Comment 2 Aaron Lu 2013-12-19 06:47:51 UTC

ping

Comment 3 Sébastien Wilmet 2013-12-19 19:22:48 UTC

I've rebooted with an old kernel, the 3.2.46, and the screen brightness is updated correctly, on each press on Fn + F8 or F9. The difference: max_brightness == 15.

Now I'll reboot on the 3.13-rc4.

Comment 4 Sébastien Wilmet 2013-12-19 19:32:19 UTC

On Linux 3.13-rc4 without video.use_native_backlight=1, the bug occurs.
With video.use_native_backlight=1, it works.

# cat /sys/class/backlight/intel_backlight/max_brightness 
4437

We can see in this directory that the brightness value is updated when pressing Fn + F8 or F9.

(the /sys/class/backlight/acpi_video0/ directory doesn't exist)

Comment 5 Aaron Lu 2013-12-20 00:57:00 UTC


*** This bug has been marked as a duplicate of bug 51231 ***

Comment 6 Sébastien Wilmet 2013-12-20 05:39:12 UTC

Note that video.use_native_backlight=1 is required, it doesn't work out-of-the-box. Is it possible to fix that?

Comment 7 Aaron Lu 2013-12-20 06:25:47 UTC

Yes, there is a patch to change the default value of use_native_backlight to 1:
http://marc.info/?l=linux-acpi&m=138620904732143&w=2
Once that is applied, you do not need anything extra.

For now, you can also use a xorg.conf file to tell X driver that the intel_backlight interface should be used instead of acpi_video0:
$ cat /etc/Xorg/Xorg.conf
Section "Device"
        Option     "Backlight"	"intel_backlight"
	Identifier  "Card0"
	Driver      "intel"
	BusID       "PCI:0:2:0"
EndSection

Comment 8 Sébastien Wilmet 2013-12-20 13:30:07 UTC

Okay, thank you for the information.

Comment 9 Aaron Lu 2014-02-17 05:12:34 UTC

Please attach the output of acpidump and dmidecode:
# acpidump > acpidump.txt
# dmidecode > dmi.txt

Comment 10 Sébastien Wilmet 2014-02-17 15:38:49 UTC

Created attachment 126431 [details]
Output of acpidump

Comment 11 Sébastien Wilmet 2014-02-17 15:39:18 UTC

Created attachment 126441 [details]
Output of dmidecode