Re: [PATCH 0/6] drm: Allow the damage helpers to handle buffer damage

[Javier Martinez Canillas]

Thomas Zimmermann <tzimmermann@xxxxxxx> writes:

Hello Thomas,

> Hi

[...]

>>> And why does it flicker? Is there old data stored somewhere?
>>>
>> 
>> It flickers because the framebuffer changed and so the damage tracking
>> is not used correctly to flush the damaged areas to the backing storage.
>
> I think I got it from the links in patch 5.  In out other drivers, 
> there's a single backing storage for each plane (for example in the 
> video memory). Here, there's a backing storage for each buffer. On page

Correct, that's what I understood too.

> flips, the plane changes its backing storage.  Our GEM buffer is up to 
> date, but the respective backing storage is missing all the intermediate 
> changes.
>
> If I'm not mistaken, an entirely different solution would be to 
> implement a per-plane back storage in these drivers.
>

I believe so but I'm not sure if that's possible since the virtio-gpu spec
defines that the VM should send a VIRTIO_GPU_CMD_RESOURCE_FLUSH to the VMM
in the host to do an update and the granularity for that is a framebuffer.

For that reason the only solution (other than forcing a full plane update
like this patch-set does) is to implement tracking suppor for buffer damage.

> Best regards
> Thomas
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat