Re: [PATCH 00/11] OvmfPkg, ArmVirtPkg: GOP driver for the VirtIo GPU (virtio-gpu-pci)

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 1 September 2016 at 20:52, Jordan Justen <jordan.l.justen@intel.com> wrote:
> On 2016-09-01 11:46:04, Laszlo Ersek wrote:
>> On 09/01/16 20:03, Jordan Justen wrote:
>>
>> > I think there would be value to have a non-VGA device that could still
>> > configure a simple framebuffer. VGA does bring a fair amount of other
>> > baggage.
>>
>> Ah, I see your point. You distinguish "VGA" from "non-VGA device with
>> framebuffer".
>>
>> For this discussion however, this distinction makes no difference. The
>> suggested "non-VGA device with framebuffer" would be broken exactly the
>> same way. In other words, it's not the "other baggage" that is broken,
>> it is the framebuffer.
>>
>
> This is only focusing on the current ARM issue. I'm just pointing out
> that I think virtio gpu without VGA, but with a framebuffer could be
> useful on IA32/X64 as well.
>
> 1. You don't have to deal with the PCI bus
>
> 2. The OS re-enumerating the PCI bus would not break the framebuffer
>

How does adding a framebuffer to virtio-gpu solve any of that?
virtio-gpu is a PCI device as well

> Is there no chance that ARM KVM might someday also be able to support
> a framebuffer?
>

There are workarounds imaginable, but none of them are feasible in
terms. A new revision of the architecture may address this, but that
will take years to turn up in real hardware.

> Obviously this is not too important for IA32/X64 OVMF, because we have
> reasonable alternatives. But, it seems like virtio gpu could be a
> significantly better option for IA32/X64 OVMF if an optional
> framebuffer was possible.
>

IIUC, not having a linear framebuffer was one of the design goals,
since it is essentially a layering violation in the virtio stack.
virtio-gpu is strictly ring based, like other virtio devices.

If you want a framebuffer, you should use virtio-vga. Adding a
framebuffer to virtio-gpu is a step back rather than a step forward.

Also, the loader->OS handover already suffers from the issues you
mention, since the PCI reconfiguration breaks GOP on almost every
platform. The reason that it is less of a concern on ARM is that most
systems use UART as the primary console.