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

[David C. Rankin]

On 11/20/2016 03:56 AM, Ralf Mardorf wrote:
> Are you using the "helper script" because
> 
>   sudo echo $(luminance) > "$dest"/brightness
> 
> doesn't work? If so, then consider to use
> 
>   echo $(luminance) | sudo tee "$dest"/brightness
> 
> to get rid of the "helper script".
> 
> Regards,
> Ralf

Thanks Ralf,

  Yes, tee redirected into /dev/null to suppress the tee output works as does:

  su -c 'command ...'

or

  sudo sh -c 'command ...'

  I noted the use of su -c in the original (the only extra steps there are
tweaking /etc/pam.d/su). I had the helper from manually setting the
brightness, e.g. sudo nvhelper.sh level (and it's a lot easier to explain "use
a helper" than bog down in a discussion of why in 'sudo echo X > file' sudo
only applies to 'echo' :)

  Whatever you like best to insure redirection is done as root. I'm just glad
to have a working backlight with the nvidia driver. Now if I can just convince
myself to stomach plasma/fw5... easier said than done...

  I also think there is probably a way to write a udev rule that does the
monitoring of acpi_video0 and changes nvidia_backlight as well. I just haven't
had time to explore that one. That would probably be the cleanest way of doing it.

  This HP laptop has been full of more surprises than I've ever had before in
Linux. My previous 3 laptops have all be Toshibas, and Dell before that. No
problems with any of them. (although I did have to use acpi_video0 for
brightness after the whatever version upgrade to X broke backlight control for
that model a couple of years ago) This laptop still won't boot grub, but
everything else works wonderfully. (the new squished screen at 1600x900 takes
getting used to as I could see more, clearer at 1440x900 on the old one, and
the physical dimensions of the old screen were actually larger than this one)

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