|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)|
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
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