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

[Anthoine Bourgeois <anthoine.bourgeois@gmail.com>]

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