UPSTREAM: drm/virtgpu api: define a dummy fence signaled event

The current virtgpu implementation of poll(..) drops events
when VIRTGPU_CONTEXT_PARAM_POLL_RINGS_MASK is enabled (otherwise
it's like a normal DRM driver).

This is because paravirtualized userspaces receives responses in a
buffer of type BLOB_MEM_GUEST, not by read(..).

To be in line with other DRM drivers and avoid specialized behavior,
it is possible to define a dummy event for virtgpu.  Paravirtualized
userspace will now have to call read(..) on the DRM fd to receive the
dummy event.

Fixes: b1079043 ("drm/virtgpu api: create context init feature")
Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20211122232210.602-2-gurchetansingh@google.com


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 7e78781d)

BUG=b:176158390, b:203009046, b:230100768
TEST=gfxbench and deqp-cts in arcvm

Signed-off-by: Rob Clark <robdclark@chromium.org>
Change-Id: I4007e202132a6e0c4dca9570efa70483bd768306
Disallow-Recycled-Builds: test-failures
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3602854


Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Chia-I Wu <olv@google.com>
Reviewed-by: Ryan Neph <ryanneph@google.com>