8086:2a42 [Asus UL80VT] Backlight control does not work with Intel integrated card, but there are entries in /sys/class/backlight

[Guillaume Millet]

It used to work with the workaround suggested at http://wiki.daviddarts.com/Ubuntu_Maverick_on_the_Asus_UL30VT#Screen_Brightness which modifies asus-brn-down.sh to use the "setpci" method.

But I had forgotten that workaround and I suspect that upgrading to Raring removed my modified scripts. So, in the original description of the bug, I thought it was a regression. But it's probably not a regression as the brightness control has apparently never worked off-the-shelf.

Not working neither with linux-image-3.9.1-030901-generic_3.9.1-030901.201305080210 from http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.9.1-saucy/

Hotkeys are detected, showkey -s:
Fn+F5:
0xe0 0x4c 0xe0 0xcc
Fn+F6:
0xe0 0x54 0xe0 0xd4

I also attach the results from tests described on https://wiki.ubuntu.com/Kernel/Debugging/Backlight.

Test with acpi_backlight=vendor:
- on 3.8.0-20.31-generic, no change. But echo 8 > /sys/class/backlight/intel_backlight/brightness makes the screen dark, moreover /sys/class/backlight/intel_backlight/max_brightness = 2583660
- on 3.9.1, no brightness change but the KDE notification pops up with only 3 levels (0, 53, 100%)

Test with video.use_bios_initial_backlight=0:
- on 3.8.0-20.31-generic, no change.

WORKAROUND: specify the backlight option in xorg.conf.

Section "Device"
    Identifier "Default Device"
    Option "Backlight" "intel_backlight"
    Driver "intel"
    BusID "PCI:0:2:0"
EndSection

WORKAROUND: On KDE Raring Ubuntu 3.8.0-30.44-generic, bumblebee removed, BIOS SATA mode set to Compatible (this disables the Intel graphics card which does not appear anymore in lspci, http://wiki.daviddarts.com/Ubuntu_Maverick_on_the_Asus_UL30VT#Nvidia_Accelerated_Graphics_Driver), only default kernel parameters, and using either nouveau or nvidia drivers:
The plasma widget for screen brightness (inside battery monitor widget) is able to change the brightness. And automatic brightness change from KDE system (when the power adaptor is unplugged) works also. In Raring, the hotkeys do not trigger any change (see bug #1225067) but this is fixed in Saucy.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: linux-image-3.8.0-20-generic 3.8.0-20.31
ProcVersionSignature: Ubuntu 3.8.0-20.31-generic 3.8.11
Uname: Linux 3.8.0-20-generic x86_64
ApportVersion: 2.9.2-0ubuntu8
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: guillaume 2490 F.... pulseaudio
 /dev/snd/controlC0: guillaume 2490 F.... pulseaudio
Date: Fri May 10 12:14:58 2013
HibernationDevice: RESUME=/dev/sda6
InstallationDate: Installed on 2010-01-19 (1207 days ago)
InstallationMedia: Kubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
MachineType: ASUSTeK Computer Inc. UL80VT
MarkForUpload: True
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.8.0-20-generic root=UUID=d92f3a31-9e9c-4c19-98be-6fbc82629a36 ro video.use_bios_initial_backlight=0 quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-3.8.0-20-generic N/A
 linux-backports-modules-3.8.0-20-generic N/A
 linux-firmware 1.106
SourcePackage: linux
UpgradeStatus: Upgraded to raring on 2013-04-27 (12 days ago)
dmi.bios.date: 01/17/2011
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 214
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: UL80VT
dmi.board.vendor: ASUSTeK Computer Inc.
dmi.board.version: 1.0
dmi.chassis.asset.tag: ATN12345678901234567
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK Computer Inc.
dmi.chassis.version: 1.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr214:bd01/17/2011:svnASUSTeKComputerInc.:pnUL80VT:pvr1.0:rvnASUSTeKComputerInc.:rnUL80VT:rvr1.0:cvnASUSTeKComputerInc.:ct10:cvr1.0:
dmi.product.name: UL80VT
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK Computer Inc.
---
ApportVersion: 2.12-0ubuntu3
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: ubuntu 2788 F.... pulseaudio
 /dev/snd/controlC0: ubuntu 2788 F.... pulseaudio
CasperVersion: 1.336
DistroRelease: Ubuntu 13.10
LiveMediaBuild: Ubuntu 13.10 "Saucy Salamander" - Alpha amd64 (20130813)
MachineType: ASUSTeK Computer Inc. UL80VT
MarkForUpload: True
Package: linux (not installed)
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: noprompt cdrom-detect/try-usb=true file=/cdrom/preseed/username.seed boot=casper initrd=/casper/initrd.lz quiet splash acpi_backlight=vendor --
ProcVersionSignature: Ubuntu 3.11.0-1.4-generic 3.11.0-rc4
RelatedPackageVersions:
 linux-restricted-modules-3.11.0-1-generic N/A
 linux-backports-modules-3.11.0-1-generic N/A
 linux-firmware 1.113
Tags: saucy
Uname: Linux 3.11.0-1-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
dmi.bios.date: 01/17/2011
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 214
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: UL80VT
dmi.board.vendor: ASUSTeK Computer Inc.
dmi.board.version: 1.0
dmi.chassis.asset.tag: ATN12345678901234567
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK Computer Inc.
dmi.chassis.version: 1.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr214:bd01/17/2011:svnASUSTeKComputerInc.:pnUL80VT:pvr1.0:rvnASUSTeKComputerInc.:rnUL80VT:rvr1.0:cvnASUSTeKComputerInc.:ct10:cvr1.0:
dmi.product.name: UL80VT
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK Computer Inc.

[Guillaume Millet (guimillet)]

sudo fwts
Running 42 tests, results appended to results.log

sudo fwts method
Running 1 tests, results appended to results.log

[Guillaume Millet (guimillet)]

dmesg | grep 'ACPI: Video'
[ 2.367054] ACPI: Video Device [VGA] (multi-head: yes rom: no post: no)
[ 2.373679] ACPI: Video Device [VGA1] (multi-head: yes rom: yes post: no)

[Guillaume Millet (guimillet)]

sudo dmidecode > dmidecode.log

[Guillaume Millet (guimillet)]

with kernel parameter acpi_backlight=vendor

ls /sys/class/backlight > vendorbacklight

[Brad Figg (brad-figg)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

Would it be possible for you to test the latest upstream kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v3.10 kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

If you are unable to test the mainline kernel, for example it will not boot, please add the tag: 'kernel-unable-to-test-upstream'.
Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.10-rc1-saucy/

[mb1248 (mb1248)]

I tried the the latest upstream kernel. The but is not fixed. Someone should add the tag: 'kernel-bug-exists-upstream'.

[Guillaume Millet (guimillet)]

v3.10-rc2 tested, still not fixed.

[Guillaume Millet (guimillet)]

v3.10-rc5 tested, no change.

[Martin Tamashiro (martintama)]

I'm using Linux Mint 15, which is based on ubuntu raring so it may work for you too. My brightness keys are working, but I had to update my BIOS to latest ver. 214. I was using ver. 206 before with no luck.

I also had to change /etc/acpi/events/asus-keyboard-backlight-up and /etc/acpi/events/asus-keyboard-backlight-down to listen to the correct event on keypress, acording to acpi_listen.

Let me know if you need more info.

[Guillaume Millet (guimillet)]

v3.11-rc1 tested, no change.

my BIOS is already ver. 214. On v3.11-rc1, key events are detected (KDE popup) but the brightness does not change.

[Guillaume Millet (guimillet)]

v3.11-rc2 tested, no change.
dmesg files without (dmesg.0) and with acpi_backlight=vendor (dmesg_acpi_backlight_vendor.1) are attached.

[Guillaume Millet (guimillet)]

v3.11-rc3 tested, no change.

[Guillaume Millet (guimillet)]

Well, I'm lost. It seems not related to linux-image, as the kernel image 3.5.0-17.28 (quantal release) does not work either. So it may come from another package update, acpi-support?

other notes:
- sudo setpci -s 00:02.0 F4.B=HH with HH between 0 and ff works.
- echo 258366 > /sys/class/backlight/intel_backlight/brightness works (values between 0 and 2583660)
- /etc/acpi/asus-keyboard-backlight.sh looks for /sys/class/leds/asus\:\:kbd_backlight. I have no such entry (acpi-support_0.141).

[penalvch (penalvch)]

Guillaume Millet, this would not come from from the package acpi-support, it's either a userspace or kernel issue. Hence, could you please confirm this issue exists with the latest development release of Ubuntu? ISO images are available from http://cdimage.ubuntu.com/daily-live/current/ . If the issue remains, could you please run the following command in the development release from a Terminal (Applications->Accessories->Terminal), as it will automatically gather and attach updated debug information to this report:

apport-collect -p linux <replace-with-bug-number>

[Guillaume Millet (guimillet)]

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[Guillaume Millet (guimillet)]

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[Guillaume Millet (guimillet)]

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[Guillaume Millet (guimillet)]

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[Guillaume Millet (guimillet)]

I also tried the daily release without acpi_backlight=vendor, but backlight control did not work.
The brightness applet reacts to the hotkeys, but the brigthness of the screen does not change.

[Guillaume Millet (guimillet)]

Was the report useful? or are other specific tests required?

[penalvch (penalvch)]

Guillaume Millet, could you please test the latest mainline kernel via http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.11-rc7-saucy/ and advise on the results?

[Guillaume Millet (guimillet)]

tested, as well as v3.11-saucy: not working. Pressing the hotkeys don't display any brightness popup and the slide in the brightness applet (through the KDE Battery monitor) does not change the screen brightness.
Do kernel developpers need more specific debug information?

[penalvch (penalvch)]

Guillaume Millet, for regression testing purposes, could you please for this in Precise release prior to Quantal enablement stack via http://old-releases.ubuntu.com/releases/precise/ ?

[Guillaume Millet (guimillet)]

Hi Christopher, I have tried ubuntu-12.04.2-desktop-amd64.iso and ubuntu-12.04-desktop-amd64.iso: the brightness applet reacts to the hotkeys but the brigthness of the screen does not change.

I thought it was working before 13.04 but I don't remember whether I tweaked something. Maybe I added acpi_backlight=vendor, shall I tried the same old-releases with acpi_backlight=vendor? Do you need me to attach dmesg report for each?

[Guillaume Millet (guimillet)]

I probably had tweaked my acpi script according to the information given at http://wiki.daviddarts.com/Ubuntu_Maverick_on_the_Asus_UL30VT#Screen_Brightness which suggests to use setpci. And probably, the modified scripts /etc/acpi/asus-brn-down.sh (and -up) were deleted during the upgrade to raring.

Apparently, it has never worked off-the-shelf and it also affects UL30VT: http://askubuntu.com/questions/327736/unable-to-adjust-backlight-on-asus-ul30vt-neither-with-fn-keys-nor-with-xbacklig.

[Guillaume Millet (guimillet)]

I have updated the description according to my last message. I think the bug is not a regression and it has never worked directly. It would be nice to fix it after 3 years of existence.

[penalvch (penalvch)]

Guillaume Millet, it looks like you disabled the discrete nvidia card in BIOS in both Raring and Saucy?

[Guillaume Millet (guimillet)]

The discrete nvidia card is not disabled in BIOS. In the first lspci.txt attached (Raring), the discrete card was disabled by the module bbswitch (https://github.com/Bumblebee-Project/Bumblebee/wiki/Power-Management). In the second lspci.txt attached (Live Saucy), the discrete card was not disabled.

[penalvch (penalvch)]

Guillaume Millet, ok. It looks like in Saucy nouveau just failed to enable the discrete card altogether.

Despite this, in your Raring install, if you uninstall Bumblebee (which isn't provided by a supported Ubuntu repository [1]), remove all non-default kernel parameters (ex. video.use_bios_initial_backlight=0), and switched to the nvidia drivers [2], are you then able to adjust your backlight without any further modifications?

[1] https://wiki.ubuntu.com/Bumblebee#Installation
[2] https://help.ubuntu.com/community/BinaryDriverHowto/Nvidia#NVIDIA_drivers_provided_by_the_Ubuntu_repositories

[Guillaume Millet (guimillet)]

On my Raring, KDE, Ubuntu 3.8.0-30.44-generic, bumblebee removed, BIOS SATA Compatible (to allow nvidia drivers to work, http://wiki.daviddarts.com/Ubuntu_Maverick_on_the_Asus_UL30VT#Nvidia_Accelerated_Graphics_Driver, note that that also disables the intel card which does not appear anymore in lspci), only default kernel parameters:
The plasma widget for screen brightness (actually battery monitor) is able to change the brightness. And automatic brightness change from KDE system (when power is unplugged) works also. However, the hotkeys do not trigger any change.
Is there any debug files that would be useful?

[penalvch (penalvch)]

Guillaume Millet, given the nvidia drivers works except via hotkeys, it would be easier to pursue a fix for this, versus fixing both nouveau not adjusting brightness correctly, and hotkeys with nouveau.

Hence, with the setup noted in https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1178796/comments/52 in please, could you please file a new report via:
ubuntu-bug linux

and include the information in https://wiki.ubuntu.com/Hotkeys/Troubleshooting .

[Guillaume Millet (guimillet)]

Well, I could file a new report with this particular setup (BIOS parameter SATA in mode Compatible, Intel graphics card disabled) if it helps to fix nouveau not adjusting brightness correctly (hotkeys with nouveau works in Precise and Saucy) . But I am not willing to keep using this setup as the nvidia card consumes more power than the Intel card.

[Guillaume Millet (guimillet)]

Filed as Bug #1225067.

[Guillaume Millet (guimillet)]

Just to correct my comment #54:
-nouveau
+i915
The goal is to fix i915 not adjusting brightness correctly.

Ideally, the nvidia card is enabled only when necessary, using either nouveau or nvidia driver, thanks to Bumblebee (which, for Saucy and newer, is provided by a supported Ubuntu repository). Then backlight control during a temporary use of the nvidia card will be filed as another bug if it appears.

[penalvch (penalvch)]

Guillaume Millet, was the problem not reproducible without using any WORKAROUNDS in a release prior to Raring?

[Guillaume Millet (guimillet)]

Christopher, I am not sure to understand your question. Did you mean, did the problem appear before Raring if the setpci method was not used? yes, for example, in 12.04 (comment #46).

I didn't try to disable the Intel card in a release prior to Raring, I suppose that situation would be similar as that reported in Bug #1225067.

[penalvch (penalvch)]

Guillaume Millet, following https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1178796/comments/57 , was the problem not reproducible without using any WORKAROUNDS in a release prior to Precise?

[Guillaume Millet (guimillet)]

The bug existed on Maverick, as noticied on http://wiki.daviddarts.com/Ubuntu_Maverick_on_the_Asus_UL30VT#Screen_Brightness.
However, today, Precise is the last release still supported on Desktop. I have not tested any other release.

[Guillaume Millet (guimillet)]

Tested Live Lucid http://old-releases.ubuntu.com/releases/lucid/ubuntu-10.04.4-desktop-amd64.iso.
Result: same as in Precise, that is, the screen brightness applet reacts to the hotkeys but the screen brigthness does not change.

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu) because there has been no activity for 60 days.]

[Guillaume Millet (guimillet)]

Tested with 3.12-saucy, same as in my last message.

[Guillaume Millet (guimillet)]

v3.12.1 tested, as well as v3.13-rc2; bug still present.

[penalvch (penalvch)]

Guillaume Millet, the issue you are reporting is an upstream one. Could you please report this problem through the appropriate channel (I would start with linux-acpi) by following the instructions _verbatim_ at https://wiki.ubuntu.com/Bugs/Upstream/kernel#KernelTeam.2BAC8-KernelTeamBugPolicies.Overview_on_Reporting_Bugs_Upstream ?

Please provide a direct URL to your post once you have made it so that it may be tracked.

Thank you for your understanding.

[Guillaume Millet (guimillet)]

issue reported upstream on linux-acpi mailing list: http://marc.info/?t=138600362800003&r=1&w=2

[Guillaume Millet (guimillet)]

Here is a workaround from Aaron Lu on linux-acpi: specify the backlight option in xorg.conf.

Section "Device"
    Identifier "Default Device"
    Option "Backlight" "intel_backlight"
    Driver "intel"
    BusID "PCI:0:2:0"
EndSection

[gmillet3 (gmillet3-linux-kernel-bugs)]

Created attachment 117421
dmesg

The screen brightness control has apparently never worked off-the-shelf on this laptop released in 2009, Asus UL80VT-A1, which is an NVIDIA Optimus laptop (2 graphic cards). The use of the discrete Nvidia card is managed by Bumblebee (https://wiki.ubuntu.com/Bumblebee). It used to work with the workaround suggested at http://wiki.daviddarts.com/Ubuntu_Maverick_on_the_Asus_UL30VT#Screen_Brightness which modifies asus-brn-down.sh to use the "setpci" method. When the hotkeys are triggered, there is no brightness change but the KDE popup notification appears.

$ ls /sys/class/backlight/
acpi_video0 acpi_video1 intel_backlight

$ cat /sys/class/backlight/intel_backlight/max_brightness
2583660
$ cat /sys/class/backlight/intel_backlight/brightness
121584

The intel_backlight interface works, by echoing a value between 0 and 2583660.

$ cat /sys/class/backlight/acpi_video0/brightness
6
$ cat /sys/class/backlight/acpi_video0/max_brightness
15
$ cat /sys/class/backlight/acpi_video0/device/device
0x2a42

$ cat /sys/class/backlight/acpi_video1/brightness
15
$ cat /sys/class/backlight/acpi_video1/max_brightness
15
$ cat /sys/class/backlight/acpi_video1/device/device
0x0a74

By echoing a value between 0 and 15, the two acpi_video interfaces do not change the screen brightness.

[gmillet3 (gmillet3-linux-kernel-bugs)]

Created attachment 117431
acpidump

[gmillet3 (gmillet3-linux-kernel-bugs)]

Created attachment 117441
dmidecode

[gmillet3 (gmillet3-linux-kernel-bugs)]

Created attachment 117451
Xorg.0.log

$ cat /etc/X11/xorg.conf

Section "Screen"
        Identifier "Default Screen"
        DefaultDepth 24
EndSection

Section "Device"
        Identifier "Default Device"
EndSection

[gmillet3 (gmillet3-linux-kernel-bugs)]

Previous thread on linux-acpi http://marc.info/?t=138600362800003&r=1&w=2

Launchpad downstream bug report on https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1178796

[aaron.lu (aaron.lu-linux-kernel-bugs)]

I saw the kernel you used is a distro kernel v3.11, is it the same case with v3.12?

[gmillet3 (gmillet3-linux-kernel-bugs)]

Same problem with 3.12.0-031200-generic from http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.12-saucy/. I can attach dmesg and Xorg.0.log, they seem similar.

[aaron.lu (aaron.lu-linux-kernel-bugs)]

Does adding acpi_osi="Linux" to kernel cmdline make any difference?

[gmillet3 (gmillet3-linux-kernel-bugs)]

No difference. The hotkeys change the value in /sys/class/backlight/acpi_video0/brightness but the brightness doesn't change.
I attach dmesg and Xorg.0.log with 3.12.0-031200-generic and acpi_osi="Linux" in case it would be useful.

[gmillet3 (gmillet3-linux-kernel-bugs)]

Created attachment 118291
dmesg with acpi_osi=Linux and kernel 3.12

[gmillet3 (gmillet3-linux-kernel-bugs)]

Created attachment 118301
Xorg.0.log with acpi_osi=Linux and kernel 3.12

[aaron.lu (aaron.lu-linux-kernel-bugs)]

I've no idea why ACPI brightness control method doesn't work.
Please add acpi_backlight=vendor to kernel cmdline, see if there is only one interface(intel_backlight) left under /sys/class/backlight. If so, I can add your system into a blacklist table.

BTW, is there a firmware update for your laptop from ASUS?

[gmillet3 (gmillet3-linux-kernel-bugs)]

With acpi_backlight=vendor, there are two interfaces: asus_laptop and intel_backlight. asus_laptop reacts like acpi_video0 did when a brightness hotkey is pressed: the value of /sys/class/backlight/asus_laptop/brightness chnages but the brightness doesn't.

The BIOS is already at the last version released by ASUS on https://www.asus.com/Notebooks_Ultrabooks/UL80Vt/#support, version 214.

[Guillaume Millet (guimillet)]

The discussion continues on https://bugzilla.kernel.org/show_bug.cgi?id=66501

[aaron.lu (aaron.lu-linux-kernel-bugs)]

Created attachment 120561
Debug patch to use native backlight for a Win7 system

Sorry for replying late.
Can you please test this patch on top of a v3.13 kernel? Thanks.

[gmillet3 (gmillet3-linux-kernel-bugs)]

Thanks. Patch tested on kernel 3.13.0-rc8 for Saucy:

$ modinfo video
filename: /lib/modules/3.13.0-031300rc8-generic/kernel/drivers/acpi/video.ko
license: GPL
description: ACPI Video Driver
author: Bruno Ducrot
srcversion: 7F3F9A0CC7554649507A11E
alias: acpi*:LNXVIDEO:*
depends:
vermagic: 3.13.0-031300rc8-generic SMP mod_unload modversions
parm: brightness_switch_enabled:bool
parm: allow_duplicates:bool
parm: use_native_backlight:bool

It doesn't seem to work and there is still a ACPI_video0 interface.

$ dmesg | grep video
[ 0.253443] pci 0000:00:02.0: Boot video device
[ 1.380146] Modules linked in: ahci(+) libahci atl1c i915(+) i2c_algo_bit drm_kms_helper video drm
[ 16.952911] asus_laptop: Backlight controlled by ACPI video driver

What other debug information can I provide?

[aaron.lu (aaron.lu-linux-kernel-bugs)]

Oh, that probably because I didn't fill in the DMI entry correctly. Can you please check the value of use_native_backlight? It's located at:
/sys/module/video/parameters/use_native_backlight
And if it is N, please add video.use_native_backlight=1 to the patched kernel's cmdline and test again. Thanks.

[gmillet3 (gmillet3-linux-kernel-bugs)]

It was N.

With the additional parameter, the acpi interface is still created:

$ dmesg | grep -i backlight
[ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.13.0-031300rc8-generic root=UUID=d92f3a31-9e9c-4c19-98be-6fbc82629a36 ro quiet splash video.use_native_backlight=1 vt.handoff=7
[ 18.806833] asus_laptop: Backlight controlled by ACPI video driver

$ cat /sys/module/video/parameters/use_native_backlight
Y

[aaron.lu (aaron.lu-linux-kernel-bugs)]

Created attachment 122671
Debug patch to use native backlight for a Win7 system, v2

Please test this patch on top of a v3.13 kernel, attach the dmesg after boot up, thanks.

[gmillet3 (gmillet3-linux-kernel-bugs)]

Created attachment 123271
dmesg with patch v2

[gmillet3 (gmillet3-linux-kernel-bugs)]

With the kernel option, dmesg is similar and it doesn't work.

[aaron.lu (aaron.lu-linux-kernel-bugs)]

Did you apply the patch? I saw your kernel cmdline has: BOOT_IMAGE=/boot/vmlinuz-3.13.0-031300-generic, is the image the patched one? I've added a print in the video module's init function and it has to be printed but I didn't see it in the attached dmesg, so I'm confused.

[gmillet3 (gmillet3-linux-kernel-bugs)]

Sorry for the late reply, I was trying to understand why the modifications did not change anything whereas I changed video.ko. Could it be about the built-in property of the module, that is, can't I compile only video.ko as described in http://www.cyberciti.biz/tips/build-linux-kernel-module-against-installed-kernel-source-tree.html ?

[aaron.lu (aaron.lu-linux-kernel-bugs)]

If video.ko is built in, then I don't think you can rmmod video and then modprobe it...

[gmillet3 (gmillet3-linux-kernel-bugs)]

Well, I'm lost. After adding some printk without any change, I deleted the module video.ko just to check if it is used... no change, the system works the same. On the other end, the kernel package installed video.ko and CONFIG_ACPI_VIDEO=m is present in /boot/config-3.13.0-031300-generic, doesn't it mean that video is a loadable module?

Moreover, lsmod displays an entry video:
video 19859 1 i915
whereas $ modprobe video
FATAL: Module video not found.

Where does that video module listed by lsmod comes from?

Could the problem be related to the bug in drm module which logs a trace in dmesg, starting with [drm:intel_pipe_config_compare] *ERROR* mismatch in gmch_pfit.lvds_border_bits (expected 32768, found 0)?

[aaron.lu (aaron.lu-linux-kernel-bugs)]

(In reply to Guillaume Millet from comment #23)
> Well, I'm lost. After adding some printk without any change, I deleted the
> module video.ko just to check if it is used... no change, the system works
> the same. On the other end, the kernel package installed video.ko and
> CONFIG_ACPI_VIDEO=m is present in /boot/config-3.13.0-031300-generic,
> doesn't it mean that video is a loadable module?
>
> Moreover, lsmod displays an entry video:
> video 19859 1 i915
> whereas $ modprobe video
> FATAL: Module video not found.
>
> Where does that video module listed by lsmod comes from?

Maybe from initrd.

>
> Could the problem be related to the bug in drm module which logs a trace in
> dmesg, starting with [drm:intel_pipe_config_compare] *ERROR* mismatch in
> gmch_pfit.lvds_border_bits (expected 32768, found 0)?

Not sure about the drm driver.

Could you just build the entire kernel tree instead of only the video module?

[gmillet3 (gmillet3-linux-kernel-bugs)]

Created attachment 126321
dmesg with patch v2

[gmillet3 (gmillet3-linux-kernel-bugs)]

It took me some time as I didn't have 11 GB free to build the entire kernel tree... Anyway, the patch works and the dmesg is attached.

[aaron.lu (aaron.lu-linux-kernel-bugs)]

OK, thanks.

[aaron.lu (aaron.lu-linux-kernel-bugs)]

I think this should be solved the same way we did for Win8 systems though this laptop's firmware doesn't claim Win8 support but Matthew doesn't agree. The ACPI video control interface is broken and the reason is beyond me, so I'll re-assign this bug to Drivers/Platform-x86 for more analysis.

Guillaume,
You can continue to use the xorg.conf to select intel_backlight for your laptop.

[gmillet3 (gmillet3-linux-kernel-bugs)]

Hi Aaron, I continue to use the xorg.conf as suggested. I wondered whether the issue could have been solved without update of this thread, so I have tried kernel 4.10.10-041010-generic from http://kernel.ubuntu.com/~kernel-ppa/mainline without the xorg.conf, but the issue is still present as initially described. I suppose that this thread or the bug status will change is something happened.

[aaron.lu (aaron.lu-linux-kernel-bugs)]

There is a new quick mechanism in kernel now.

Can you try adding acpi_backlight=native to kernel cmdline? With this cmdline option, you should have only one interface under /sys/class/backlight that is intel_backlight and xorg.conf modification isn't necessary. If everything works, I can add your machine to a quirk table for this to happen automatically so that you do not need to add that cmdline option.

[gmillet3 (gmillet3-linux-kernel-bugs)]

Hi Aaron,
I have just tried the native module option on 4.4.0-92 generic Ubuntu kernel (10-Aug-2017), after removing the xorg.conf modification, and it works. Thanks.

[gmillet3 (gmillet3-linux-kernel-bugs)]

Hi Aaron, I have just installed Debian Buster, kernel 4.19.0-5-amd64 #1 SMP Debian 4.19.37-5+deb10u1. Without the cmdline option, the backlight control does not work. Has UL80VT been added to the quirk table you mentioned?