Re: [PATCH 6.1.y,6.4.y] drm/virtio: Conditionally allocate virtio_gpu_fence

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Sep 12, 2023 at 12:35:34PM +0000, Alyssa Ross wrote:
> From: Gurchetan Singh <gurchetansingh@chromium.org>
> 
> 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 expecting
> 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.
> 
> In addition, VIRTGPU_EXECBUF_RING_IDX is checked when creating a
> DRM event object.  VIRTGPU_CONTEXT_PARAM_POLL_RINGS_MASK is
> already defined in terms of per-context rings.  It was theoretically
> possible to create a DRM event on the global timeline (ring_idx == 0),
> if the context enabled DRM event polling.  However, that wouldn't
> work and userspace (Sommelier).  Explicitly disallow it for
> clarity.
> 
> Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
> Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> # edited coding style
> Link: https://patchwork.freedesktop.org/patch/msgid/20230707213124.494-1-gurchetansingh@chromium.org
> (cherry picked from commit 70d1ace56db6c79d39dbe9c0d5244452b67e2fde)
> Signed-off-by: Alyssa Ross <hi@alyssa.is>
> ---
>  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 30 +++++++++++++++-----------
>  1 file changed, 18 insertions(+), 12 deletions(-)

Both patches applied, thanks.

greg k-h