Re: [Qemu-devel] [PATCH] ati-vga: i2c fix

[BALATON Zoltan]

Hello,

On Mon, 18 Mar 2019, Gerd Hoffmann wrote:
> > > A more correct model would probably be to create two i2c busses for
> > > that, then hook up the ddc to one of them (possibly depending on a
> > > config option).
> >
> > Isn't it enough to only emulate the DVI port DDC then?
>
> Well, strictly speaking the radion has 4 i2c busses and the most correct
> way to emulate them is hooking up 4 busses.  But in practice it probably
> doesn't matter much for the guest whenever we don't emulate the unused
> busses or whenever we emulate a i2c bus with no devices connected ...

Right, emulating the ports and corresponding DDC as present but no monitor 
connected would be more correct. However we don't emulate the second 
display controller or flat panel and there may be cards without additional 
connectors so guests should cope with those not present. So unless this 
found to cause a problem for some guests I'd keep the code simple for now 
and not emulate empty ports. It's a complex enough device without that.

Does it work with the latest patch for you? I could not make Linux driver 
recognise the card yet so if you have some settings that's needed for this 
you could share those. It may also need changes to vgabios but I'm not 
familiar with that so I hope you can help with that. I've found the r128 X 
driver needs a VBE BIOS function to access DDC as mentioned in the commit 
message.

Regards,
BALATON Zoltan