drm/virtio: batch display update commands.

When the driver submits multiple commands in a row it makes sense to
notify the host only after submitting the last one, so the host can
process them all at once, with a single vmexit.

Add functions to enable/disable notifications to allow that.  Use the
new functions for primary plane updates.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20191212125346.8334-3-kraxel@redhat.com

drivers/gpu/drm/virtio/virtgpu_drv.h

@@ -183,6 +183,9 @@ struct virtio_gpu_device {
 	struct kmem_cache *vbufs;
 	bool vqs_ready;
 
+	bool disable_notify;
+	bool pending_notify;
+
 	struct ida	resource_ida;
 
 	wait_queue_head_t resp_wq;
@@ -335,6 +338,9 @@ void virtio_gpu_dequeue_ctrl_func(struct work_struct *work);
 void virtio_gpu_dequeue_cursor_func(struct work_struct *work);
 void virtio_gpu_dequeue_fence_func(struct work_struct *work);
 
+void virtio_gpu_disable_notify(struct virtio_gpu_device *vgdev);
+void virtio_gpu_enable_notify(struct virtio_gpu_device *vgdev);
+
 /* virtio_gpu_display.c */
 int virtio_gpu_framebuffer_init(struct drm_device *dev,
 				struct virtio_gpu_framebuffer *vgfb,

drivers/gpu/drm/virtio/virtgpu_plane.c

@@ -146,6 +146,8 @@ static void virtio_gpu_primary_plane_update(struct drm_plane *plane,
 		return;
 	}
 
+	virtio_gpu_disable_notify(vgdev);
+
 	vgfb = to_virtio_gpu_framebuffer(plane->state->fb);
 	bo = gem_to_virtio_gpu_obj(vgfb->base.obj[0]);
 	if (bo->dumb)
@@ -177,6 +179,8 @@ static void virtio_gpu_primary_plane_update(struct drm_plane *plane,
 				      plane->state->src_y >> 16,
 				      plane->state->src_w >> 16,
 				      plane->state->src_h >> 16);
+
+	virtio_gpu_enable_notify(vgdev);
 }
 
 static int virtio_gpu_cursor_prepare_fb(struct drm_plane *plane,

drivers/gpu/drm/virtio/virtgpu_vq.c

@@ -404,8 +404,12 @@ static void virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
 	}
 	notify = virtio_gpu_queue_ctrl_buffer_locked(vgdev, vbuf, vout);
 	spin_unlock(&vgdev->ctrlq.qlock);
-	if (notify)
-		virtqueue_notify(vgdev->ctrlq.vq);
+	if (notify) {
+		if (vgdev->disable_notify)
+			vgdev->pending_notify = true;
+		else
+			virtqueue_notify(vgdev->ctrlq.vq);
+	}
 
 	if (sgt) {
 		sg_free_table(sgt);
@@ -413,6 +417,21 @@ static void virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
 	}
 }
 
+void virtio_gpu_disable_notify(struct virtio_gpu_device *vgdev)
+{
+	vgdev->disable_notify = true;
+}
+
+void virtio_gpu_enable_notify(struct virtio_gpu_device *vgdev)
+{
+	vgdev->disable_notify = false;
+
+	if (!vgdev->pending_notify)
+		return;
+	vgdev->pending_notify = false;
+	virtqueue_notify(vgdev->ctrlq.vq);
+}
+
 static void virtio_gpu_queue_ctrl_buffer(struct virtio_gpu_device *vgdev,
 					 struct virtio_gpu_vbuffer *vbuf)
 {