Re: [PATCH] OvmfPkg/QemuVideoDxe: map framebuffer as write-combining/non-executable

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

[...]
>>
>> (1) When we added VirtioGpuDxe to the ArmVirtPkg platforms, the only
>> reason I didn't propose removing QemuVideoDxe from the same platforms
>> was that QemuVideoDxe was usable on QEMU/TCG, and I figured it wouldn't
>> hurt to keep it.
>>
>> Other than that, I see zero point in using this driver on ARM. (And,
>> apparently, it does hurt to keep it.)
>>
>> Can we please consider simply removing this driver from the ArmVirtPkg
>> platforms? (And then some now-conditional compilation could be
>> simplified in the driver too!)
>>
>
> It is actually quite useful in TCG mode, and the fact that QEMU
> currently allows unaligned accesses to device memory is not something
> we should be relying upon.
>

Actually, I managed to confuse myself here. The only thing lacking
when running with virtio-gpu rather than VGA is efifb support, due to
the fact that the framebuffer is no longer directly addressable. efifb
is a useful hack on bare metal systems that lack a real framebuffer
driver, but it is hardly something to care deeply about on VMs.

So I am going to change my mind, and agree with Laszlo: let's remove
QemuVideoDxe from ArmVirtQemu; the longer we wait, the more difficult
it becomes, and only TCG users that rely on a GOP protocol being
exposed with direct framebuffer access are going to be affected in the
first place (if any such use cases exist)

Laszlo: any ideas or suggestions you may want to share before I start
working on this?

-- 
Ard.