Fixing X220 Video The Right Way

matt sendtomatt at gmail.com
Tue Feb 26 01:54:43 UTC 2013


On 02/25/13 10:30, John Baldwin wrote:
>
> Is there a better place to "correct" the ACPI_PATH that gets stored in
> vgapci's ivar? Is there already a tunable I can use to fix this?
> vgapci's ivar is set by the PCI address.  Do you have multiple vgapci devices?
>
No, just one. I think that the DSDT is very creative on recent Lenovos
(read: broken). There are multiple video devices defined, with
"functional" calls that nonetheless don't work to actually do anything.
The acpi_get_handle() call in acpi_video returns a handle that has no
active outputs and doesn't have any control over the brightness. The
other path can control brightness.

Here's a related discussion on Linux, I'm not sure how much applies
other than the situation discussed:
http://comments.gmane.org/gmane.linux.acpi.devel/57228

The same thing happens on AGP thinkpads, I believe, based on Mitsuru
Iwasaki's comment a long time ago to an X220 thread.

Matt



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