[SeaBIOS] [PATCH] Support more than one vga card

[Glauber Costa]

On Wed, 2011-05-04 at 00:51 +0200, Sebastian Herbszt wrote:
> Glauber Costa wrote:
> > On Wed, 2011-05-04 at 00:31 +0200, Sebastian Herbszt wrote:
> >> Glauber Costa wrote:
> >> > On Wed, 2011-05-04 at 00:02 +0200, Sebastian Herbszt wrote:
> >> >> Anthony Liguori wrote:
> >> >> > On 05/03/2011 03:23 PM, Sebastian Herbszt wrote:
> >> >> >> Glauber Costa wrote:
> >> >> >>> It is theorectically possible for a system to have more than
> >> >> >>> one pci vga card. In particular, I am interested in the use of SGAbios
> >> >> >>> as a pci device, alongside of a normal vga bios in QEMU.
> >> >> >>
> >> >> >> Can't SGAbios be loaded as an option rom without this change?
> >> >> > 
> >> >> > But then you're loading it as a legacy ROM which is fairly ugly and 
> >> >> > requires additional SeaBIOS hackery.
> >> >> 
> >> >> Why is this ugly and which additional hackery does it need?
> >> >> SGAbios is a legacy ROM; the PNP header is disabled and there is no PCIR.
> >> > 
> >> > It is, but does not need to be (I've also patched sgabios to include a
> >> > PCIR). Since it is a device, it is nice to have it plugged it to a bus.
> >> > If for nothing else, for discovering capabilities - A guest using
> >> > sgabios this way is now aware that it has a double-head system.
> >> 
> >> I don't think "it is a device", more likely a functionality. SGAbios doesn't add a new
> >> device/hardware to the system.
> > 
> > This depends on how you model it. One can think that this functionality
> > is achieved by hooking a device into the system. "Hooking a device" is
> > how most functionality is achieved in real systems anyway.
> > 
> >> Do you plan to add a new (emulated) PCI device and deploy SGAbios thru its BAR?
> > Yes
> >> Do you plan to add support for "Google Memory Console"?
> > No.
> > 
> >> 
> >> > Also, let us not focus only in the specifics: Having two pci vga cards
> >> > is a real possibility, there's even a use case for that, as anthony
> >> > mentioned.
> >> 
> >> If you call the init function of two vga roms, will the last one win and hook int 10h?
> > 
> > Yes.
> 
> This might not always be the desired case. How can i control which card wins?

Bus enumeration order, only.
But that's a good question. Maybe we should come up with a method other
than bus enumeration for that. But at the tip of my tongue, none come to
mind.

> > And this is totally orthogonal to whether it is loaded as a pci device,
> > or in vgaroms/
> > The statement is true for both methods.
> 
> Shouldn't VGAbdf be set to the last (the winning) card then?
That's certainly better, you are right.

> 
> > In the specific case of sgabios, it chains the int10h calls to whatever
> > was there before, which is, IMHO, a very sane thing.
> 
> Sebastian
>