Backlight in console changes to minimum when switching from xorg to console.
But when switching back from console to xorg, brightness goes back to max as it was before switching.
Initial boot keeps maximum brightness in console through the boot process.
Fn+brightness keys (ThinkPad T410) are functional to increase and decrease brightness, both in console and in xorg.
kernel commandline "acpi_backlight=vendor" keeps brightness level the same in console and in xorg, but disable brightness buttons (Fn+Home and Fn+End in my case).
zcat /proc/config.gz | grep -i think
# CONFIG_THINKPAD_ACPI_DEBUGFACILITIES is not set
# CONFIG_THINKPAD_ACPI_DEBUG is not set
$ zgrep -i fb_backlight /proc/config.gz
# CONFIG_FB_BACKLIGHT is not set
# lsmod | grep think
thinkpad_ec 3503 2 hdaps,tp_smapi
thinkpad_acpi 53325 0
ls -1 /sys/class/backlight/
When in X mode, turn on backlight debug message by:
# cd /sys/kernel/debug/dynamic_debug
# echo 'module backlight +pft' > control
[ 179.294484]  brightness_store: backlight: set brightness to 0
[ 179.606036]  brightness_store: backlight: set brightness to 15
[ 183.627956]  brightness_store: backlight: set brightness to 15
ps aux | grep 3209
root 3098 0.0 0.0 12380 2260 pts/0 S+ 15:51 0:00 grep --colour=auto 3209
root 3209 1.1 0.8 228012 33208 tty7 Ssl+ 15:30 0:15 /usr/bin/X -nolisten tcp -br -deferglyphs 16 vt07 -auth /var/run/slim.auth
initial workup done at https://bugzilla.kernel.org/show_bug.cgi?id=79541
I'm having the same issue, except that the screen stays dark after going back to X, as well as after resuming from suspend.
I'm running Arch Linux with a hybrid graphics setup using the open source intel and radeon drivers. I have three interfaces in /sys/class/backlight.
$ ls /sys/class/backlight
acpi_video0 acpi_video1 intel_backlight
The issue appeared when upgrading xf86-video-intel from version 2.9.11 to 2.9.12.