Hi Gerd,
On Thu, Jul 29, 2021 at 01:16:57AM -0700, Vivek Kasireddy wrote:
This feature enables the Guest to wait to know when a resource is completely consumed by the Host.
virtio spec update?
What are the exact semantics?
[Kasireddy, Vivek] As of now, this is still a RFC version. If everyone (Weston Upstream, drm upstream and you) agree that this is a reasonable way to solve https://gitlab.freedesktop.org/wayland/weston/-/issues/514 then I'd go ahead and send out the spec updates and cleaner versions of these patches -- with more documentation.
Why a new command? Can't you simply fence one of the commands sent anyway (set_scanout probably for page-flip updates)?
[Kasireddy, Vivek] Yes, I think I could add a fence (and an out_fence) to set-scanout-blob.
(feature flag is probably needed even in case we don't need a new command to make sure the host sends the completion when processing the command is actually done, i.e. in case of qemu the recently added fence support is there).
[Kasireddy, Vivek] The recently added fence support was for resource_flush and specifically for GTK-UI or similar backends. I tried using the same mechanism for Wayland-UI backend but ran into the above Weston issue. This feature (OUT_FENCE) is a potential solution for this issue.
Thanks, Vivek
take care, Gerd