Bug 41672

Summary:	backlight control will not work on Lenovo V570
Product:	ACPI	Reporter:	Bill Pemberton (wfp5p)
Component:	Power-Video	Assignee:	Zhang Rui (rui.zhang)
Status:	CLOSED CODE_FIX
Severity:	normal	CC:	rui.zhang, wfp5p
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	3.1-rc3 and others	Subsystem:
Regression:	No	Bisected commit-id:
Attachments:	dmesg from 3.1-rc3 boot on Lenovo V570 acpidump output for Lenovo V570 Ugly hack that just disables multihead detection

Description Bill Pemberton 2011-08-24 19:25:14 UTC

No backlight options will be available on a Lenovo V570.  I've tried it with several different kernel versions including 3.1-rc3.  In all cases dmesg has the error  ACPI Error: Current brightness invalid. 

It appears the kernel believes the machine is multi-headed.  It does the right thing for the first head it sees and then gets the invalid brightness on the second head which causes it to assume acpi brightness won't work.  The laptop has the standard external D-sub connector for an external monitor, but there is nothing connected to it.  In fact, if I make the ugly hack of commenting out the multihead check in acpi_video_bus_check() then backlight control works fine.

I'll attach the acpidump, dmesg, and ugly hack.

Comment 1 Bill Pemberton 2011-08-24 19:27:06 UTC

Created attachment 69942 [details]
dmesg from 3.1-rc3 boot on Lenovo V570

Comment 2 Bill Pemberton 2011-08-24 19:27:47 UTC

Created attachment 69952 [details]
acpidump output for Lenovo V570

Comment 3 Bill Pemberton 2011-08-24 19:30:18 UTC

Created attachment 69962 [details]
Ugly hack that just disables multihead detection

This is just to make it clear what I meant when I say disabling multihead detection.  I know this is in no way a fix, just documenting my troubleshooting steps.

Comment 4 Zhang Rui 2012-11-28 07:18:29 UTC

IMO, with your patch, acpi_video_bus_check() fails and it makes acpi_video driver fails to load.

so will you please set CONFIG_ACPI_VIDEO=n and see if the backlight still works?

btw, how do you change the backlight, via hotkeys?

Comment 5 Bill Pemberton 2012-11-28 13:47:46 UTC

I know my patch wasn't a fix for anything, it was just a hack to turn off the multihead complaint.

On the kernel that was current when this bug was filed, there was no backlight control at all that would work.  Using a current 3.6 kernel (at least, using the 3.6 kernel that comes with Fedora 17), I can control backlight by echoing the value I want in the appropriate /sys/class/backlight file.  As far as I know things are fine using 3.6 -- I don't use the laptop much (it's not mine).

I think this can be closed as fixed somewhere post 3.1.