Re: [Qemu-devel] [PATCH] virtio-pci: make pci bar layout more flexible.

[Michael S. Tsirkin]

On Wed, Mar 04, 2015 at 11:55:50AM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> > > VirtIOPCIProxy subclasses which need additional pci bars, such as
> > > virtio-vga, just need to make sure they register the additinal bars
> > > before initializing virtio-pci, so the superclass can see the registered
> > > bars and shuffle around the virtio bars accordingly.
> > 
> > I think I prefer we just DTRT and keep same layouts for everyone by
> > default: isn't there a layout that is good for everybody?
> 
> I want bar #2 for the vga framebuffer for virtio-vga.  Which conflicts
> with bar #2 being used for the modern bar in todays code.

OK, and IIUC you are saying that using bar #2 for that is a requirement for
vga to work?

> We can move the modern bar to #4 for everybody, then we'll have:
> 
>   #0 -- legacy i/o
>   #1 -- msix
>   #2 -- unused (by virtio)
>   #3 -- unused (by virtio)
>   #4 -- modern mem
>   #5 -- modern mem too (because it's 64bit).
> 
> That'll leave bars #2 + #3 free, for additional bars (1x 64bit or 2x
> 32bit) such as vga framebuffer if needed.

Yes, that's fine with me.

> > I know this means we'll leave BAR0 unused for modern devices but that
> > does not seem too bad.
> 
> Yep, no technical reason against it, although it IMHO looks nicer.
> 
> cheers,
>   Gerd

If we run into a problem, we'll be able to reshuffle it all easily.

-- 
MST