Re: [Qemu-devel] selecting VIRTIO_INPUT and VIRTIO_VGA

[Alexander Graf <agraf@suse.de>]

On 07/20/15 21:06, Laszlo Ersek wrote:
> Cc'ing Alex
>
> On 07/13/15 12:15, Paolo Bonzini wrote:
>>
>> On 13/07/2015 09:32, Gerd Hoffmann wrote:
>>>> and virtio-vga is only compiled on 64-bit Intel?
>>> There is virtio-gpu-pci ...
>>>
>>> Any specific reason why we need vga compatibility on !x86?
>> I was actually thinking about 32-bit x86. :)  I agree that !x86 is not
>> necessary.
> I disagree :)
>
> (This is actually my more important followup to this thread; the other
> message I just couldn't resist sending.)
>
> Gerd recently contributed virtio-vga support to OvmfPkg/QemuVideoDxe:
>
> https://github.com/tianocore/edk2/commit/94210dc9
>
> That support depends on vga compat. All fine.
>
> What's probably not obvious is that I had ported
> PcAtChipsetPkg/PciHostBridgeDxe to ArmVirtPkg -- which drives Alex's
> generic PCIe host bridge, exposed on qemu-system-(arm|aarch64) -M virt
> -- and included OvmfPkg/QemuVideoDxe in the ArmVirtQemu.dsc build too.
>
> That means you can currently stick a -device VGA into -M virt, and it
> will work. Since OvmfPkg/QemuVideoDxe recognizes virtio-vga (see edk2

For some definition of work, yes :). It will work perfectly fine with 
TCG, you will run into cache coherency problems with KVM because the 
guest maps MMIO regions (like the vram) as uncached while QEMU accesses 
it as cached.

> 94210dc9 again), and the driver is included by ArmVirtQemu.dsc, I think
> it would be probably useful to build the device model for arm/aarch64
> targets too.
>
> See also QEMU commit 332261de2b (together with its parent commits).

I agree. Also, as far as I understood Marc, his hope was that the fix to 
halfway working VGA emulation would be virtio-gpu.


Alex