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This seems to be a recurring question, but none of the solutions I found here and there seem to work for me. So here are the facts:

  • Toshiba Satellite P855-30D
  • Nvidia 640M
  • BIOS 1.50
  • Ubuntu 13.04 64 bits
  • Always at full backlight

I've tried the 4 variants given here: http://ubuntuforums.org/showthread.php?t=2139397&p=12621502&viewfull=1#post12621502 with no luck. Some of them make /sys/class/backlight/* empty. But even when it is populated, whatever I put in /sys/class/backlight/acpi_video0/brightness is ignored.

The brightness keys are fn-F2 and fn-F3 on this model. fn-F2 opens the Power Statistics, fn-F3 crashes X. Other function keys work fine.

Edit after upgrading the BIOS to latest 6.70 :

GRUB_CMDLINE_LINUX=""
/sys/class/backlight/ is populated
/sys/class/backlight/acpi_video0/max_brightness:100

changing /sys/class/backlight/acpi_video0/brightness has no effect

GRUB_CMDLINE_LINUX="acpi_osi=Linux acpi_backlight=vendor"
/sys/class/backlight/ is empty

No param to change

GRUB_CMDLINE_LINUX="acpi_osi="
/sys/class/backlight/ is populated
/sys/class/backlight/acpi_video0/max_brightness:7

changing /sys/class/backlight/acpi_video0/brightness has no effect

GRUB_CMDLINE_LINUX="acpi_osi=\"!Windows 2012\""
/sys/class/backlight/ is populated
/sys/class/backlight/acpi_video0/max_brightness:7

changing /sys/class/backlight/acpi_video0/brightness has no effect

Opened a bug https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1199062 since conventional solutions are not working.

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I assume that every time that you modified your /etc/default/grub you also ran sudo update-grub and rebooted? That's a common mistake that people forget is necessary if they do anything to the GRUB parameters. –  gravity May 30 '13 at 20:51
    
Yes I did. Another idea ? –  Julien C. May 31 '13 at 17:31
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1 Answer

I found a solution : use nvidia's proprietary drivers. As soon as the driver is loaded, the settings scrollbar is working.

Not the hotkeys though... I'll have a look into that.

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