https://bugzilla.kernel.org/show_bug.cgi?id=60545
Bug ID: 60545
Summary: acpi_video0/brightness:0 after VT switch
Product: ACPI
Version: 2.5
Kernel Version: 3.10
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Power-Video
Assignee: [email protected]
Reporter: [email protected]
Regression: No
I was able to reproduce the following report on the laptops:
- Lenovo T400,
- Lenovo T500 and
- Lenovo X230.
The problem:
I'm having an X server configured to use the external monitor only (LVDS off).
If I switch from that X server to a console (or to another X server which uses
the LVDS), then the brightness of the LVDS stays at very low level (text is
unreadable).
When the issue happens, it's possible to raise the brightness by:
- pressing the brightness keys or
- writing a value > 0 into /sys/class/backlight/acpi_video0/brightness.
It doesn't happen if I pass "acpi_backlight=vendor" to the kernel. A dmesg log
for this case will be attached too.
The following attachments are dmesg logs that have been made with the kernel
parameters:
- drm.debug=0x2 (DRM_UT_DRIVER),
- acpi.debug_layer=0x10000000 (ACPI_VIDEO_COMPONENT) and
- acpi.debug_level=0x20000004 (ACPI_LV_VERBOSE_INFO | ACPI_LV_INFO).
Additionally they include the output of my script to monitor the
/sys/class/brightness/*/* states, this output can found by searching for "XXX",
and a few comments I've made to document dmesg log lines occuring due to user
interaction, my comments can be found by searching for "YYY".
(Basically, those pimped dmesg log have been created by:
- capturing the output of my script into a file,
- attach the dmesg output to that file,
- sort that file `sort -k2 -bn $file` and
- add my comments.)
So the following attachments (dmesg logs) are:
1. for the case this report is about,
2. with acpi_backlight=vendor, where this bug doesn't happen, and
3. for documenting another discovery I've made:
o If I setup the X server as described (external only, LVDS off),
o press the keys to raise the brightness (I can't see any changes as the
LVDS is and stays off) and
o switch to the console, then the brightness is at a normal level.
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