Created attachment 196491 [details] acpidump output It is not possible to change screen backlight. A workaround is to add a flag acpi_osi=
dmesg and lspci please, and please also list /sys/class/backlight, thanks.
/sys/class/backlight acpi_video0 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight lspci: 00:00.0 Host bridge: Intel Corporation 3rd Gen Core processor DRAM Controller (rev 09) 00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09) 00:14.0 USB controller: Intel Corporation 7 Series/C210 Series Chipset Family USB xHCI Host Controller (rev 04) 00:16.0 Communication controller: Intel Corporation 7 Series/C210 Series Chipset Family MEI Controller #1 (rev 04) 00:1a.0 USB controller: Intel Corporation 7 Series/C210 Series Chipset Family USB Enhanced Host Controller #2 (rev 04) 00:1b.0 Audio device: Intel Corporation 7 Series/C210 Series Chipset Family High Definition Audio Controller (rev 04) 00:1c.0 PCI bridge: Intel Corporation 7 Series/C210 Series Chipset Family PCI Express Root Port 1 (rev c4) 00:1c.3 PCI bridge: Intel Corporation 7 Series/C210 Series Chipset Family PCI Express Root Port 4 (rev c4) 00:1d.0 USB controller: Intel Corporation 7 Series/C210 Series Chipset Family USB Enhanced Host Controller #1 (rev 04) 00:1f.0 ISA bridge: Intel Corporation HM76 Express Chipset LPC Controller (rev 04) 00:1f.2 SATA controller: Intel Corporation 7 Series Chipset Family 6-port SATA Controller [AHCI mode] (rev 04) 00:1f.3 SMBus: Intel Corporation 7 Series/C210 Series Chipset Family SMBus Controller (rev 04) 01:00.0 Network controller: Intel Corporation Centrino Advanced-N 6235 (rev 24) 02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 06)
Created attachment 196521 [details] dmesg
The firmware claims to support Win8, so the ACPI video driver will not register acpi_videoX interface if you do not add any acpi_osi kernel cmdline options and the intel_backlight is supposed to provide this functionality. Please test if manually change backlight through intel_backlight works: # cd /sys/class/backlight/intel_backlight # cat max_brightness XXX # echo some_value_smaller_than_max > brightness see if backlight changes.
There is no change in backlight when I change the value in intel_backlight/brightness It may help or not, but previously I was testing it with ubuntu-patched kernels in similar way, here is the track, https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1516320 Let me know if I can help you somehow with it.
The acpi_osi= cmdline option is a big hammer and may affect many things, so please test: 1 acpi_backlight=video cmdline option alone, see if acpi_videoX interface works; 2 acpi_osi="!Windows 2012" cmdline option alone, see if acpi_videoX interface works. Thanks.
In both cases, backlight works properly.
If case 1 acpi_videoX interface works, then intel_backlight interface should also work since in the Win8 case(the firmware default case if we do not pass any acpi_osi= string), the acpi_videoX interface's backlight control is relayed to GPU driver. Can you please double check: boot with "acpi_backlight=video drm.debug=0xe" cmdline option, and manually change brightness file of both acpi_videoX and intel_backlight see if backlight change works, and after the test, capture dmesg and upload it, thanks.
When I boot with acpi_backlight=video drm.debug=0xe I can change backlight with /sys/class/backlight/acpi_video0/brightness however manipulating with /sys/class/backlight/intel_backlight doesn't make any effect. Dmesg is as attachment - dmesg_20151209.txt
Created attachment 196981 [details] dmesg when acpi_backlight=video drm.debug=0xe
The dmesg doesn't seem have drm.debug=0xe cmdline option set, and it seems to be taken right after boot? Can you please capture two dmesgs that: 1 with "acpi_backlight=video drm.debug=0xe" cmdline option, after boot, adjust backlight level through acpi_videoX interface and then capture the dmesg; 2 with "acpi_backlight=video drm.debug=0xe" cmdline option, after boot, adjust backlight level through intel_backlight interface and then capture the dmesg. Thanks.
Created attachment 196991 [details] dmesg with acpi_video0
Created attachment 197001 [details] dmesg intel backlight
Sorry, I probably missed update-grub that time... It is done in both cases (but I can't see acpi output in dmesg like for intel backlight) - here are these changes /sys/class/backlight/acpi_video0# cat max_brightness 95 /sys/class/backlight/acpi_video0# echo 30 > brightness /sys/class/backlight/acpi_video0# echo 18 > brightness /sys/class/backlight/acpi_video0# echo 42 > brightness It works in acpi, but doesn't work in intel_backlight.
Thanks for the log. So from the log, the GPU driver did modify the backlight: [ 97.100108] [drm:intel_backlight_device_update_status] updating intel_backlight, brightness=3000/4650 [ 97.100120] [drm:intel_panel_actually_set_backlight] set backlight PWM = 3414 But it just doesn't work. Jani, Do you want to take a look at it? If no clue, I can add a quirk to force the firmware interface for this laptop(its firmware claims Win8). Thanks.
Adam, Please attach your dmi info: # dmidecode > dmi.info I'll quirk your laptop to use acpi_video interface by default.
Created attachment 198311 [details] dmidecode
Created attachment 198361 [details] quirk to use acpi_video Patch is prepared on top of latest linus git tree, may also apply cleanly on older kernels.
I have built a new kernel with this patch, rebooted without flags, it works - I can change backlight in /sys/class/backlight/acpi_video0
Patch sent out with all of you CC-ed. https://patchwork.kernel.org/patch/7931931/
commit 49eb5208220a9eef7529decbdefd95e4b94a928b Author: Aaron Lu <aaron.lu@intel.com> Date: Wed Dec 30 13:11:24 2015 +0800 ACPI / video: Add a quirk to force acpi-video backlight on SAMSUNG 530U4E/540U4E