Re: Less strict requirements for video device detection

[Zhang Rui <rui.zhang@intel.com>]

On Thu, 2009-08-20 at 17:14 +0800, Stefan Bader wrote:
> Hardware: Acer 6920G (from a bug report)
> 
> Another case of a broken BIOS. In this case there are several definitions for 
> video bus devices but only one has _DOS and _DOD defined. All other definitions 
> only have _DOD.

I have seen such kind of BIOS too.

> In the past (2.6.27) _ADR was not evaluated to make sure of using a present 
> video device, but with that bug brightness could be changed.
> 
> Now the video bus having _DOS and _DOD is detected as not being present. The 
> other definitions are not considered because they are lacking the _DOS method.
> Using the attached patch, would cause the detection code to consider the other 
> definitions and has been tested to enable backlight control.
> 

> Would this be an acceptable approach?

I think so. I generated a similar patch before, but didn't sent it out
for some reason.
My suggestion is that we should also print out a warning message if _DOS
is missed, what do you think?

thanks,
rui

>  From the ACPI spec it rather sounds like 
> _DOD and _DOS must be present for a device for display switching and _DOS would 
> indicate possible backlight control as well. So the question might not be so 
> much is it the right thing than is it safe enough to allow more compatibility 
> with broken implementations without causing other problems...
> 
> -Stefan
>