Comment 56 for bug 267241

On Fri, Mar 6, 2009 at 9:34 PM, Bryce Harrington
<email address hidden> wrote:
> I've done some analysis into this bug (as well as a number of other
> related dual-card bugs) this week.  This patch changes the behavior such
> that when it gets into this error condition, rather than giving up and
> erroring out, it should make X select the card with the highest busid.
>
> The use case I'm imagining here is where a user is having problems with
> their on-board video and have purchased a second card to override it.
> Don't know whether that use case is a good match to folks' issues here,
> so am open to discussion on that.
>

Correct me if I am wrong but I *think* that would not be the most
common use case - in case of machines having built-in video and a
discrete card, the BIOS completely disables one of them depending on
what is chosen in BIOS. (At least the HP desktop I had did this - it
had Intel GMA on-board and when I put in a nv 8400 GS - I was allowed
to choose one - the other was completely 'gone' for the OS).
(I have no idea what the case is with Laptops using 2 cards which
allow for runtime switching between low-power / high-power - but since
I have heard of no problems with MacBooks which have this feature - I
suspect that only one is visible.) Your patch seems like it will pick
the last one seen - whether or not it will work obviously depends on
whether or not people have connected output to the last one seen by
Xorg.

The most common case in relation to this issue would be where people
actually have 2 discrete cards and BIOS allows one to be set to
primary - the second one is still visible to the OS. Figuring out what
the BIOS's notion of Primary/Secondary is may be easier I think to
determine where to output. I will put the 2nd card back in my
workstation and see if I can find any clues.

Parag