[arch-general] Nvidia backlight control - acpi_video0/brightness changes - display doesn't?

[David C. Rankin]

On 11/17/2016 04:31 PM, David C. Rankin wrote:
> All,
> 
>   Laptop: HP 8760w, Quadro 3000M, nvidia-340xx packages.
> 
>   The driver works perfectly (no errors in Xorg.0.log), but I have no way to
> control the screen brightness. I've followed the suggestions in:
> 
> https://wiki.archlinux.org/index.php/NVIDIA/Tips_and_tricks
> 
>   but I still have no backlight control. Using the laptop function keys, the
> values in /sys/class/backlight/acpi_video0/brightness are properly set, e.g.
> 
> $ cat /sys/class/backlight/acpi_video0/brightness
> 8
> 
> (now tap the [func][F9], brightness lower, twice)
> 
> $ cat /sys/class/backlight/acpi_video0/brightness
> 6
> 
> (actual_brightness value tracks brightness)
> 
> $ cat /sys/class/backlight/acpi_video0/max_brightness
> 20
> 
>   This works with OR without /etc/X11/xorg.conf.d/20-nvidia.conf:
> 
>         Option "RegistryDwords" "EnableBrightnessControl=1"
> 
>   Does anyone have any suggestions on anything else to try before I start
> loading the aur nvidia-bl or nvidiabl packages? I don't mind adding more
> software, but if there are a few more tweaks to try before going that route, I
> would like to try them first. Anybody get backlight working with a similar
> model laptop?
> 

  Let me add to this, that powerdevil is seeing the screen brightness changes
and Udev is evidently applying them correctly. For example, pressing the
function key to raise/lower brightness seems to generate the correct log entries:

Nov 17 23:36:37 seidr org_kde_powerdevil[710]: powerdevil: Screen brightness
value:  6
Nov 17 23:36:37 seidr org_kde_powerdevil[710]: powerdevil: Screen brightness
value max:  20
Nov 17 23:36:37 seidr dbus[334]: [system] Activating service
name='org.kde.powerdevil.backlighthelper' (using servicehelper)
Nov 17 23:36:37 seidr org_kde_powerdevil[710]: powerdevil: set screen
brightness value:  7
Nov 17 23:36:37 seidr org_kde_powerdevil[710]: powerdevil: Screen brightness
value max:  20
Nov 17 23:36:37 seidr dbus[334]: [system] Successfully activated service
'org.kde.powerdevil.backlighthelper'
Nov 17 23:36:37 seidr org_kde_powerdevil[710]: powerdevil: Udev device changed
"/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/acpi_video0"
"/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/acpi_video0"

  And, as noted above, the values in
/sys/class/backlight/acpi_video0/brightness are changing as they should.

  I'll give both the aur packages a try (I have both built -- but the nvidiabl
package is currently disowwned and needs a maintainer if anyone is interested)

-- 
David C. Rankin, J.D.,P.E.