Re: [PATCH v6 0/3] Add sync object UAPI support to VirtIO-GPU driver

On Wed, May 3, 2023 at 10:07 AM Gurchetan Singh
[off-list ref] wrote:

On Mon, May 1, 2023 at 8:38 AM Dmitry Osipenko [off-list ref] wrote:

quoted

On 4/16/23 14:52, Dmitry Osipenko wrote:

quoted

We have multiple Vulkan context types that are awaiting for the addition
of the sync object DRM UAPI support to the VirtIO-GPU kernel driver:

 1. Venus context
 2. Native contexts (virtio-freedreno, virtio-intel, virtio-amdgpu)

Mesa core supports DRM sync object UAPI, providing Vulkan drivers with a
generic fencing implementation that we want to utilize.

This patch adds initial sync objects support. It creates fundament for a
further fencing improvements. Later on we will want to extend the VirtIO-GPU
fencing API with passing fence IDs to host for waiting, it will be a new
additional VirtIO-GPU IOCTL and more. Today we have several VirtIO-GPU context
drivers in works that require VirtIO-GPU to support sync objects UAPI.

The patch is heavily inspired by the sync object UAPI implementation of the
MSM driver.

Gerd, do you have any objections to merging this series?

We have AMDGPU [1] and Intel [2] native context WIP drivers depending on
the sync object support. It is the only part missing from kernel today
that is wanted by the native context drivers. Otherwise, there are few
other things in Qemu and virglrenderer left to sort out.

[1] https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21658
[2] https://gitlab.freedesktop.org/digetx/mesa/-/commits/native-context-iris

I'm not saying this change isn't good, just it's probably possible to implement the native contexts (even up to even VK1.2) without it.  But this patch series may be the most ergonomic way to do it, given how Mesa is designed.  But you probably want one of Mesa MRs reviewed first before merging (I added a comment on the amdgpu change) and that is a requirement [a].

[a] "The userspace side must be fully reviewed and tested to the standards of that user space project. For e.g. mesa this means piglit testcases and review on the mailing list. This is again to ensure that the new interface actually gets the job done." -- from the requirements

tbh, the syncobj support is all drm core, the only driver specifics is
the ioctl parsing.  IMHO existing tests and the two existing consumers
are sufficient.  (Also, considering that additional non-drm
dependencies involved.)

If this was for the core drm syncobj implementation, and not just
driver ioctl parsing and wiring up the core helpers, I would agree
with you.

BR,
-R
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