Re: Less strict requirements for video device detection (v3)

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

Acked-by: Zhang Rui <rui.zhang@intel.com>

On Mon, 2009-08-24 at 22:44 +0800, Stefan Bader wrote:
> Zhang Rui wrote:
> > 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")?
> 
> I am not biased on that.
> 
> -Stefan
> > 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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