Comment 0 for bug 1518473

With nvidia-352 (and for that matter nvidia-346), the /sys/class/backlight interface is broken.

Writing to /sys/class/backlight/acpi_video0/brightness has no effect, and reading from it returns a value that does not necessarily reflect the current brightness.

I don't know when exactly this broke in the Nvidia driver, but I do know that not that long ago it worked because the system76-driver uses this to restore the previous backlight brightness level during boot. I believe this still worked with nvidia-343 and perhaps also worked in early nvidia-346 versions.

This problem is somewhat masked because with Ubuntu (Unity), unity-settings-daemon has two code paths for setting the brightness:

1) Using /sys/class/backlight

2) Using xrandr, which as far as I can tell takes (roughly) the same approach as the `xbacklight` command line tool

However, approach (2) does not work with Ubuntu GNOME because gnome-settings-daemon has dropped this code ((it dropped gnome-settings-daemon/gsd-rr*).

I've started digging into the dkms module source code, but haven't come up with anything yet. Of course, there is a chance the problem is in the closed proprietary bits.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: nvidia-352 352.63-0ubuntu0.15.10.1
ProcVersionSignature: Ubuntu 4.2.0-18.22-generic 4.2.3
Uname: Linux 4.2.0-18-generic x86_64
NonfreeKernelModules: nvidia
.proc.driver.nvidia.registry: Binary: ""
.proc.driver.nvidia.version:
 NVRM version: NVIDIA UNIX x86_64 Kernel Module 352.63 Sat Nov 7 21:25:42 PST 2015
 GCC version: gcc version 5.2.1 20151010 (Ubuntu 5.2.1-22ubuntu2)
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Nov 20 15:01:42 2015
DistUpgraded: Fresh install
DistroCodename: wily
DistroVariant: ubuntu
DkmsStatus:
 bbswitch, 0.7, 4.2.0-18-generic, x86_64: installed
 fwts-efi-runtime-dkms, 15.09.00, 4.2.0-18-generic, x86_64: installed
 nvidia-352, 352.63, 4.2.0-18-generic, x86_64: installed
GraphicsCard:
 NVIDIA Corporation GM204M [GeForce GTX 970M] [10de:1618] (rev a1) (prog-if 00 [VGA controller])
   Subsystem: CLEVO/KAPOK Computer Device [1558:7701]
MachineType: System76, Inc. Serval WS
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.2.0-18-generic.efi.signed root=UUID=d68b8062-f67c-495c-8c16-f2e11d9a9916 ro quiet splash
SourcePackage: nvidia-graphics-drivers-352
UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev'
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 06/09/2015
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 1.03.03RSY2
dmi.board.asset.tag: Tag 12345
dmi.board.name: Serval WS
dmi.board.vendor: System76, Inc.
dmi.board.version: serw8-17g
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 9
dmi.chassis.vendor: System76, Inc.
dmi.chassis.version: Serval WS
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1.03.03RSY2:bd06/09/2015:svnSystem76,Inc.:pnServalWS:pvrserw8-17g:rvnSystem76,Inc.:rnServalWS:rvrserw8-17g:cvnSystem76,Inc.:ct9:cvrServalWS:
dmi.product.name: Serval WS
dmi.product.version: serw8-17g
dmi.sys.vendor: System76, Inc.
modified.conffile..etc.modprobe.d.nvidia.352.hybrid.conf: [deleted]
version.compiz: compiz 1:0.9.12.2+15.10.20151015-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.64-1
version.libgl1-mesa-dri: libgl1-mesa-dri 11.0.2-1ubuntu4
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 11.0.2-1ubuntu4
version.nvidia-graphics-drivers: nvidia-graphics-drivers-* N/A
version.xserver-xorg-core: xserver-xorg-core 2:1.17.2-1ubuntu9
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.9.2-1ubuntu1
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.5.0+git20150819-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20150808-0ubuntu4
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.11-1ubuntu3
xserver.bootTime: Fri Nov 20 08:41:35 2015
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:

xserver.version: 2:1.17.2-1ubuntu9