drm/virtio: fix ring free check

If the virtio device supports indirect ring descriptors we need only one
ring entry for the whole command.  Take that into account when checking
whenever the virtqueue has enough free entries for our command.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200207064653.14403-1-kraxel@redhat.com

drivers/gpu/drm/virtio/virtgpu_debugfs.c

@@ -47,6 +47,7 @@ static int virtio_gpu_features(struct seq_file *m, void *data)
 
 	virtio_add_bool(m, "virgl", vgdev->has_virgl_3d);
 	virtio_add_bool(m, "edid", vgdev->has_edid);
+	virtio_add_bool(m, "indirect", vgdev->has_indirect);
 	virtio_add_int(m, "cap sets", vgdev->num_capsets);
 	virtio_add_int(m, "scanouts", vgdev->num_scanouts);
 	return 0;

drivers/gpu/drm/virtio/virtgpu_drv.h

@@ -193,6 +193,7 @@ struct virtio_gpu_device {
 
 	bool has_virgl_3d;
 	bool has_edid;
+	bool has_indirect;
 
 	struct work_struct config_changed_work;
 

drivers/gpu/drm/virtio/virtgpu_kms.c

@@ -159,6 +159,9 @@ int virtio_gpu_init(struct drm_device *dev)
 	if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_EDID)) {
 		vgdev->has_edid = true;
 	}
+	if (virtio_has_feature(vgdev->vdev, VIRTIO_RING_F_INDIRECT_DESC)) {
+		vgdev->has_indirect = true;
+	}
 
 	DRM_INFO("features: %cvirgl %cedid\n",
 		 vgdev->has_virgl_3d ? '+' : '-',

drivers/gpu/drm/virtio/virtgpu_vq.c

@@ -330,6 +330,9 @@ static void virtio_gpu_queue_ctrl_sgs(struct virtio_gpu_device *vgdev,
 	bool notify = false;
 	int ret;
 
+	if (vgdev->has_indirect)
+		elemcnt = 1;
+
 again:
 	spin_lock(&vgdev->ctrlq.qlock);