[PATCH v2] drm/virtio: conditionally allocate virtio_gpu_fence

[Gurchetan Singh]

On Wed, Jun 28, 2023 at 8:58 AM Gurchetan Singh
<gurchetansingh at chromium.org> wrote:
>
> We don't want to create a fence for every command submission.  It's
> only necessary when userspace provides a waitable token for submission.
> This could be:
>
> 1) bo_handles, to be used with VIRTGPU_WAIT
> 2) out_fence_fd, to be used with dma_fence apis
> 3) a ring_idx provided with VIRTGPU_CONTEXT_PARAM_POLL_RINGS_MASK
>    + DRM event API
> 4) syncobjs in the future
>
> The use case for just submitting a command to the host, and expected
> no response.  For example, gfxstream has GFXSTREAM_CONTEXT_PING that
> just wakes up the host side worker threads.  There's also
> CROSS_DOMAIN_CMD_SEND which just sends data to the Wayland server.
>
> This prevents the need to signal the automatically created
> virtio_gpu_fence.
>
> Signed-off-by: Gurchetan Singh <gurchetansingh at chromium.org>
> Reviewed-by: <dmitry.osipenko at collabora.com>
> ---
>  v2: Fix indent (Dmitry)
>
>  drivers/gpu/drm/virtio/virtgpu_submit.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_submit.c b/drivers/gpu/drm/virtio/virtgpu_submit.c
> index cf3c04b16a7a..8c7e15c31164 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_submit.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_submit.c
> @@ -168,9 +168,13 @@ static int virtio_gpu_init_submit(struct virtio_gpu_submit *submit,
>
>         memset(submit, 0, sizeof(*submit));
>
> -       out_fence = virtio_gpu_fence_alloc(vgdev, fence_ctx, ring_idx);
> -       if (!out_fence)
> -               return -ENOMEM;
> +       if ((exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_OUT) ||
> +           ((exbuf->flags & VIRTGPU_EXECBUF_RING_IDX) &&
> +           (vfpriv->ring_idx_mask & BIT_ULL(ring_idx))) ||
> +           exbuf->num_bo_handles)
> +               out_fence = virtio_gpu_fence_alloc(vgdev, fence_ctx, ring_idx);
> +       else
> +               out_fence = NULL;
>
>         err = virtio_gpu_fence_event_create(dev, file, out_fence, ring_idx);
>         if (err) {
> --

Ping for additional reviews or merge.

> 2.41.0.162.gfafddb0af9-goog
>