vhost-user-gpu: check backend for EDID support

EDID has been enabled by default, but the backend may not implement
it (such as the contrib backend). This results in extra warnings and
potentially other issues in the guest.

The option shouldn't probably have been added to VIRTIO_GPU_BASE, but
it's a bit too late now, report an error and disable EDID when it's
not available.

Fixes: 0a71966 ("edid: flip the default to enabled")

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210204105232.834642-2-marcandre.lureau@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/display/vhost-user-gpu.c

@@ -555,6 +555,12 @@ vhost_user_gpu_device_realize(DeviceState *qdev, Error **errp)
     if (virtio_has_feature(g->vhost->dev.features, VIRTIO_GPU_F_VIRGL)) {
         g->parent_obj.conf.flags |= 1 << VIRTIO_GPU_FLAG_VIRGL_ENABLED;
     }
+    if (virtio_has_feature(g->vhost->dev.features, VIRTIO_GPU_F_EDID)) {
+        g->parent_obj.conf.flags |= 1 << VIRTIO_GPU_FLAG_EDID_ENABLED;
+    } else {
+        error_report("EDID requested but the backend doesn't support it.");
+        g->parent_obj.conf.flags &= ~(1 << VIRTIO_GPU_FLAG_EDID_ENABLED);
+    }
 
     if (!virtio_gpu_base_device_realize(qdev, NULL, NULL, errp)) {
         return;