Good. Now for the next test build. What I did this time was add a new
file:

  /sys/bus/acpi/devices/TOS1900:00/backlight

which I will simply call "the backlight file." This file will let you
read and write values directly to the register that is supposed to fix
the backlight issues after suspend. This way we can try a variety of
things without requiring new builds each time. The build is at:

http://people.canonical.com/~sforshee/lp935778/toshiba-acpi-
dkms_0.6~lp935778v201203281156_all.deb

Please start with the following things in order. It's probably a good
idea to do this over ssh so you can continue trying things if the
backlight turns off.

1. After installing the new driver, reboot. Use cat to read the value of
the backlight file after rebooting and let me know what the value is.

2. Write 0 to the backlight file (i.e. echo 0 | sudo tee .../backlight).
What happens? Can you change the brigtness via the acpi_video0 and
toshiba backlights after doing this?

3. Write 1 to the backlight file. What happens? Can you change the
brightness via the acpi_video0 and toshiba backlights after doing this?

4. Write 0 to the backlight file, then suspend and resume. Does either
of the methods of suspending cause a hang?

5. Reboot, then suspend and resume the machine. What's the value of the
backlight file after resuming?

6. Write 1 to the backlight file. Do either of the acpi_video0 and
toshiba backlight interfaces work after doing this?

7. If the backlights do not work after 6, try writing a new brightness
to /sys/class/backlight/toshiba/brightness and then writing 1 to the
backlight file. Does anything happen?

Feel free to try anything additional that occurs to you. Thanks!

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https://bugs.launchpad.net/bugs/935778

Title:
  Toshiba R840 - brightness controls work on first boot, but do nothing
  after suspend/resume

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