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

[Christian Klaue]

Hi,


your xrandr --brightness solution only works on oled screens. Those
don't have a backlight. From a quick search it looks like you have a
LCD, right?


I am having exactly the same problem with my HP. I went as far as
decompiling the ACPI bios. When I tried to compile it again, it threw a
huge amount of errors. So I gave up. I didn't find any solution for my
problem. I even tried other distros. I am still kind of convinced the
error is in the ACPI module(s) of your UEFI. If you try to blame HP (as
many people on their forum did before) they will ask you to test on
Windows. Unfortunately there it works. The newest BIOS update doesn't
fix the problem for my toy.

I am lucky to have an OLED. Please keep me updated if you find a
solution.

regards,

Christian

On Sat, 2016-11-19 at 03:09 -0600, David C. Rankin wrote:
> On 11/19/2016 02:35 AM, Patrick Burroughs (Celti) via arch-general
> wrote:
> > acpi_backlight=vendor is the default, acpi_backlight=none is
> > invalid.
> > The option you are looking for is acpi_backlight=video, which takes
> > the
> > backlight control away from the vendor driver and hands it back
> > over to
> > the standard ACPI backlight driver. This will generally solve the
> > issue
> > you are having.
> > 
> > ~Celti
> 
> Damn,
> 
>   And it worked so well that way :(  Thank you for identifying the
> brightness/backlight issue. The Backlight wiki is where I first got
> the
> acpi_backlight=none suggestion, see:
> 
> https://wiki.archlinux.org/index.php/Backlight#Kernel_command-line_op
> tions
> 
>   I've tried the acpi_backlight=video, and still no-joy (at least I
> still have
> the acpi_video0 sysfs interface with that setting). The nice pop-up
> still
> appears and shows the brightness adjustment, but the screen never
> changes.
> (same symptoms as before)
> 
>   How is adjusting xrandr --brightness bad compared to adjusting
> /sys/class/backlight/acpi_video0/brightness?? I understand setting
> xrandr
> --brightness greater than 1.0 will draw additional power, etc.., but
> how is
> setting it between 0.0 and 1.0 different than doing it with acpi? I'm
> just
> trying to get it sorted out in my mind to understand the difference
> between
> setting:
> 
>   /sys/class/backlight/acpi_video0/brightness
> 
> and
> 
>   xrandr --output LVDS-0 --brightness $foo
> 
>   I'll go search to see if I can find the difference, but if you have
> a
> favorite link, I'd appreciate the help.
>