Bug 80987 - backlight in console changes to minimum when switching from xorg to console
Summary: backlight in console changes to minimum when switching from xorg to console
Status: NEW
Alias: None
Product: libbacklight
Classification: Unclassified
Component: general (show other bugs)
Version: unspecified
Hardware: x86-64 (AMD64) Linux (All)
: medium normal
Assignee: Matthew Garrett
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Reported: 2014-07-07 03:27 UTC by Dmitri
Modified: 2014-08-22 10:55 UTC (History)
0 users

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Description Dmitri 2014-07-07 03:27:24 UTC
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=m 
CONFIG_THINKPAD_ACPI_ALSA_SUPPORT=y 
# CONFIG_THINKPAD_ACPI_DEBUGFACILITIES is not set 
# CONFIG_THINKPAD_ACPI_DEBUG is not set 
CONFIG_THINKPAD_ACPI_UNSAFE_LEDS=y 
CONFIG_THINKPAD_ACPI_VIDEO=y 
CONFIG_THINKPAD_ACPI_HOTKEY_POLL=y

$ 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/
acpi_video0
intel_backlight

When in X mode, turn on backlight debug message by:
# cd /sys/kernel/debug/dynamic_debug
# echo 'module backlight +pft' > control
# dmesg
[  179.294484] [3209] brightness_store: backlight: set brightness to 0
[  179.606036] [3209] brightness_store: backlight: set brightness to 15
[  183.627956] [3209] 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
Comment 1 Dmitri 2014-07-07 06:08:22 UTC
x11-base/xorg-server-1.15.99.903
sys-kernel/gentoo-sources-3.15.3
Comment 2 tfnwq 2014-08-22 10:55:46 UTC
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.


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