Re: [PATCH] virtio-vga: fix virtio-vga bar ordering

[Anthoine Bourgeois]

On Wed, Apr 22, 2020 at 12:46:57PM +0200, Gerd Hoffmann wrote:
> > This fix exchange the modern io bar with the modern memory bar,
> > replacing the msix bar that is never impacted anyway.
>
> Well, msix was placed in bar 4 intentionally.  That keeps bar 1 (default
> msix location) free, so we have the option to turn bar 0 (vga compat
> vram) into a 64bit bar without shuffling around things.

That's a really good reason I didn't think of.
Just a question, why didn't we choose the virtio-vga order to avoid
shuffling from the beginning? Vga came after and we keep the
compatibility ?

> > -    vpci_dev->msix_bar_idx = 4;
>
> Please don't.
>
> > +    vpci_dev->modern_io_bar_idx = 4;
>
> We can use bar 5 instead.
>
> Alternatively just throw an error saying that modern-pio-notify is not
> supported.

As you like. I sent a v2 with modern_io_bar_idx to 5 but I can do a v3
with an error thrown.

> > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > index 4cb784389c..9c5efaa06e 100644
> > --- a/hw/virtio/virtio-pci.c
> > +++ b/hw/virtio/virtio-pci.c
> > @@ -1705,6 +1705,7 @@ static void virtio_pci_realize(PCIDevice *pci_dev, Error 
> > **errp)
> >       *
> >       *   region 0   --  virtio legacy io bar
> >       *   region 1   --  msi-x bar
> > +     *   region 2   --  virtio modern io bar
> >       *   region 4+5 --  virtio modern memory (64bit) bar
>
> Separate patch please.  Also worth noting that the modern io bar is off
> by default.

Done.

Thank you,
Anthoine