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 21:23, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> 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

... of performance

> 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.