Kernel Bug Tracker – Bug 11647
Multiple virtual ACPI backlight devices created for a single LCD
Last modified: 2008-11-17 00:31:50 UTC
Distribution: Ubuntu 8.10
Hardware Environment: Dell Inspiron 1420, XPS M1330, Inspiron 1525
It appears that the DSDT from these machines is causing multiple virtual backlight devices to get created in /sys. Likely this is because the DSDT will work both with the discrete and uma case.
Steps to reproduce:
Browse /sys tree for directory containing backlight devices. Observe that multiple backlight devices exist and are functional.
Created attachment 18042 [details]
Here is the DSDT from an Inspiron 1420.
Created attachment 18043 [details]
/sys tree showing multiple backlight devices
the _BCM methods of the two video device, which is used to control the backlight, are the same.
So I don't think the AML code is well written.
also there is a patch set from matthew which should fix the duplicate device problem, please give it a try.
in order to get the source code, you need to:
> git-clone git://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-acpi-2.6 acpi_test
> git-branch -r
> git-branch --track test origin/test
> git-checkout test
*** Bug 11557 has been marked as a duplicate of this bug. ***
Hi Zhang Rui:
I added this patch to my local video.ko:
It does work as expected and restores all 8 video levels.
This patch has already been in acpi test tree.
exactly what patch what release fixes this issue?
Is this related to bug 9995, for which we tried a patch
and then reverted it?
Yes it's that exact same patch that was applied and reverted.
The patch was dropped because it caused a regression:
The ACPI video backlight I/F for T61 doesn't work any more.
we've root caused that this is a BIOS bug,
and use dmi check to prevent this BOX from using ACPI video backlight I/F.
All this is done in thomas' "video detection" patch set.
It seems that len forgot to take thomas' "video detection" patch set in Andi's tree.
Thomas is going to post them again. :p
Re-assign this bug to thomas, and we can close it once the patches are sent out.
patch shipped in 2.6.28-rc4