Re: Less strict requirements for video device detection (v2)

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

On Fri, 2009-08-21 at 18:00 +0800, Stefan Bader wrote:
> Zhang Rui wrote:
> > 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?
> 
> Some indication about the problem can't hurt. Probably not in 
> acpi_is_video_device as that would trigger for even unused devices.
> So I added a warning to acpi_video_bus_check for the case when _DOS is missing. 

how about using printk(KERN_WARNING FW_BUG "blabla")?

thanks,
rui

> The case of _DOS being present but _DOD not might also be worth a warning but 
> (though the check in acpi_is_video_device prevented this) would have been 
> accepted by the current code.
> -Stefan
> 
> > 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
> >>
> > 
> 
> 

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