Bug 66501

Created attachment 117431 [details]
acpidump

Created attachment 117441 [details]
dmidecode

Created attachment 117451 [details]
Xorg.0.log

$ cat /etc/X11/xorg.conf

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


Section "Device"
        Identifier      "Default Device"
EndSection

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

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

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.

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

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.

Created attachment 118291 [details]
dmesg with acpi_osi=Linux and kernel 3.12

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

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?

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.

Created attachment 120561 [details]
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.

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?

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.

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

Created attachment 122671 [details]
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.

Created attachment 123271 [details]
dmesg with patch v2

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

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.

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 ?

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

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)?

(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?

Created attachment 126321 [details]
dmesg with patch v2

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.

OK, thanks.

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.

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.

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.

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.

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?