On laptop on card AMD, screen brightness backlight isn't memorized between sessions (systemd-backlight)

[Tamir]

HOW TO REPRODUCE:
  1. Boot a laptop (on example my laptop on base Dual core AMD A6-4400M APU with Radeon HD Graphics 7670m) with Ubuntu 15.04 (systemd).
  2. Set a different screen backlight brightness level.
  3. Reboot.

RESULT:
  Backlight is not memorized.

Description laptop:
CPU~Dual core AMD A6-4400M APU with Radeon HD Graphics (-MCP-) speed/max~2000/2700 MHz Kernel~3.19.0-15-generic x86_64 Up~1:19 Mem~1798.2/3724.2MB HDD~500.1GB(10.5% used) Procs~208 Client~Shell inxi~2.2.16
iv@iv-pc:~$ inxi -v5
System: Host: iv-pc Kernel: 3.19.0-15-generic x86_64 (64 bit gcc: 4.9.2)
           Desktop: Unity 7.3.2 (Gtk 3.14.12-0ubuntu2)
           Distro: Ubuntu 15.04 vivid
Machine: System: SAMSUNG product: 355V4C/356V4C/3445VC/3545VC v: P09AAN.031.CP
           Mobo: SAMSUNG model: NP355V5X-S01RU v: BOARD 00
           Bios: American Megatrends v: P09AAN date: 07/04/2013
CPU: Dual core AMD A6-4400M APU with Radeon HD Graphics (-MCP-) cache: 2048 KB
           flags: (lm nx sse sse2 sse3 sse4_1 sse4_2 sse4a ssse3 svm) bmips: 10780
           clock speeds: max: 2700 MHz 1: 2700 MHz 2: 2400 MHz
Memory: Using dmidecode: you must be root to run dmidecode
Graphics: Card-1: Advanced Micro Devices [AMD/ATI] Trinity [Radeon HD 7520G]
           bus-ID: 00:01.0
           Card-2: Advanced Micro Devices [AMD/ATI] Thames [Radeon HD 7500M/7600M Series]
           bus-ID: 01:00.0
           Display Server: X.Org 1.17.1 drivers: ati,radeon (unloaded: fbdev,vesa)
           Resolution: 1366x768@60.1hz
           GLX Renderer: Gallium 0.4 on AMD ARUBA
           GLX Version: 3.0 Mesa 10.5.2 Direct Rendering: Yes

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: systemd 219-7ubuntu3
ProcVersionSignature: Ubuntu 3.19.0-15.15-generic 3.19.3
Uname: Linux 3.19.0-15-generic x86_64
ApportVersion: 2.17.2-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Apr 29 17:16:22 2015
InstallationDate: Installed on 2015-04-29 (0 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
MachineType: SAMSUNG ELECTRONICS CO., LTD. 355V4C/356V4C/3445VC/3545VC
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.19.0-15-generic root=UUID=3cdab672-0213-4aa9-8bb8-6b5a44b121b9 ro quiet splash vt.handoff=7
SourcePackage: systemd
UdevLog: Error: [Errno 2] Нет такого файла или каталога: '/var/log/udev'
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/04/2013
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: P09AAN
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: NP355V5X-S01RU
dmi.board.vendor: SAMSUNG ELECTRONICS CO., LTD.
dmi.board.version: BOARD REVISION 00
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 9
dmi.chassis.vendor: SAMSUNG ELECTRONICS CO., LTD.
dmi.chassis.version: 0.1
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP09AAN:bd07/04/2013:svnSAMSUNGELECTRONICSCO.,LTD.:pn355V4C/356V4C/3445VC/3545VC:pvrP09AAN.031.CP:rvnSAMSUNGELECTRONICSCO.,LTD.:rnNP355V5X-S01RU:rvrBOARDREVISION00:cvnSAMSUNGELECTRONICSCO.,LTD.:ct9:cvr0.1:
dmi.product.name: 355V4C/356V4C/3445VC/3545VC
dmi.product.version: P09AAN.031.CP
dmi.sys.vendor: SAMSUNG ELECTRONICS CO., LTD.

[Martin Pitt (pitti)]

Indeed the log says

апр. 29 15:48:07 username-pc systemd-backlight[442]: Failed to get backlight or LED device 'backlight:acpi_video0': No such file or directory

Can you please give me the output of

    grep -r . /sys/class/backlight/*

Are you using the free driver or the AMD proprietary one? On several boards the backlight is directly hardwired to the brightness buttons and they can't be controlled through software. If you press the brightness keys, do you get a notification bubble for that which shows the current value?

[Tamir (sugip)]

> Are you using the free driver or the AMD proprietary one?
On the laptop is only free driver supplied with kernel 3.19.

> If you press the brightness keys, do you get a notification bubble for that which shows the current value?
Yes, a notice displayed on the current value of the brightness of the screen.
The output (grep -r . /sys/class/backlight/*) is attached.

[Martin Pitt (pitti)]

OK, thanks. So it seems there is a broken acpi_video0 which doesn't appear in the grep. Can you please give me the output of

  ls -l /sys/class/backlight/

? If that's a broken symlink or so, then systemd-backlight@backlight:acpi_video0.service is okay to fail. However, there should be another one for radeon_bl0 -- can you please give me the output of

 systemctl --all|grep backlight

? It would also be helpful if you could could do a full boot, change brightness level, reboot, and then attach /var/log/syslog.

Thanks!

[Tamir (sugip)]

Martin Pitt, excuse me, probably I did not get to collect the necessary information is now no suitable laptop with an appropriate system.

[Launchpad Janitor (janitor)]

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

[Raphaël Droz (raphael-droz)]

This bug do exist
- with radeon driver(s) [radeonsi in my case]
- on some AMD hardware (Kaveri [Radeon R5 Graphics])
- is well known and explained:
* https://bbs.archlinux.org/viewtopic.php?id=193130
* https://askubuntu.com/questions/662799/laptop-backlight-sets-to-maximum-at-startup-xubuntu-15-04

Either X apps only handle brightness through a hardcoded /sys path, then:
- it should be documented
- radeon driver developpers should explain why they do not use it

Either X apps can handle various brightness interfaces, then:
- they should explain how and where to configure it

I do have a working radeon_bl0 sysfs backlight interface (the only one I have), but there seem that no software using it out there.

[Raphaël Droz (raphael-droz)]

side note: I don't think this bug has anything to do with systemd

[Martin Pitt (pitti)]

If you think this is a bug in systemd-backlight, the questions in comment #5 still apply.

[Launchpad Janitor (janitor)]

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

[Raphaël Droz (raphael-droz)]

I do have a radeon_bl0 symlink inside /sys/class/backlight/ pointing to a valid path: /sys/devices/pci0000:00/0000:00:01.0/drm/card0/card0-eDP-1/radeon_bl0
I do not use systemd.

Handling of radeon_bl0 is probably an the issue for *another* subsystem, most probably Xorg, udev or ACPI (= the same package that currently handle the acpi_video0 file (which one is it?)