Comment 26 for bug 451282

pauls (paulatgm) wrote :

I wonder if there was a change in how acpi records / sets brightness and gnome-power-manager was not updated to realize it.

I notice 2 different kernel locations on my system for brightness.

One is /sys/devices/virtual/backlight/acpi_video0/brightness and has the value of 0 on boot up. This seems strange because the lcd is at maximum brightness.

The other is /sys/devices/virtual/backlight/acpi_video0/actual_brightness and has the value of 7 on boot up. On my system, 7 is the maximum.

I suspect on suspend | hibernate that gnome-power-manager is saving "brightness" rather than "actual_brightness" and restoring that upon resume.

So, I added this little script to /etc/rc.local to set them the same.

brt=`cat /sys/devices/virtual/backlight/acpi_video0/brightness`
abrt=`cat /sys/devices/virtual/backlight/acpi_video0/actual_brightness`
if (( $brt != $abrt )) ; then
echo $abrt > /sys/devices/virtual/backlight/acpi_video0/brightness
fi

Now, on my first suspend the bug does not occur.

I'm not sure if this will be the same for everyone. To find out your own brightness, just search /sys/ with this command:

paul :~$ find /sys/ -iname '*bright*'
/sys/devices/virtual/backlight/acpi_video0/brightness
/sys/devices/virtual/backlight/acpi_video0/actual_brightness
/sys/devices/virtual/backlight/acpi_video0/max_brightness
/sys/devices/pci0000:00/0000:00:1e.0/0000:03:01.1/leds/mmc0::/brightness
/sys/devices/pci0000:00/0000:00:1e.0/0000:03:01.1/leds/mmc0::/max_brightness
/sys/module/video/parameters/brightness_switch_enabled

If your locations are different, then change /etc/rc.local to the different values for yours.

regards,