struct cx8802_dev *dev = video_drvdata(file);
        struct cx88_core  *core = dev->core;
 
+       if (vb2_is_busy(&dev->vb2_mpegq))
+               return -EBUSY;
+       if (core->v4ldev && (vb2_is_busy(&core->v4ldev->vb2_vidq) ||
+                            vb2_is_busy(&core->v4ldev->vb2_vbiq)))
+               return -EBUSY;
        vidioc_try_fmt_vid_cap(file, priv, f);
        core->width = f->fmt.pix.width;
        core->height = f->fmt.pix.height;
        struct cx8802_dev *dev = video_drvdata(file);
        struct cx88_core *core = dev->core;
 
-       cx88_set_tvnorm(core, id);
-       return 0;
+       return cx88_set_tvnorm(core, id);
 }
 
 static const struct v4l2_file_operations mpeg_fops =
 
        u32 bdelay,agcdelay,htotal;
        u32 cxiformat, cxoformat;
 
+       if (norm == core->tvnorm)
+               return 0;
+       if (core->v4ldev && (vb2_is_busy(&core->v4ldev->vb2_vidq) ||
+                            vb2_is_busy(&core->v4ldev->vb2_vbiq)))
+               return -EBUSY;
+       if (core->dvbdev && vb2_is_busy(&core->dvbdev->vb2_mpegq))
+               return -EBUSY;
        core->tvnorm = norm;
        fsc8       = norm_fsc8(norm);
        adc_clock  = xtal;
 
 
        if (0 != err)
                return err;
+       if (vb2_is_busy(&dev->vb2_vidq) || vb2_is_busy(&dev->vb2_vbiq))
+               return -EBUSY;
+       if (core->dvbdev && vb2_is_busy(&core->dvbdev->vb2_mpegq))
+               return -EBUSY;
        dev->fmt = format_by_fourcc(f->fmt.pix.pixelformat);
        core->width = f->fmt.pix.width;
        core->height = f->fmt.pix.height;
        struct cx8800_dev *dev = video_drvdata(file);
        struct cx88_core *core = dev->core;
 
-       cx88_set_tvnorm(core, tvnorms);
-
-       return 0;
+       return cx88_set_tvnorm(core, tvnorms);
 }
 
 /* only one input in this sample driver */
 
        dev->fmt = format_by_fourcc(V4L2_PIX_FMT_BGR24);
 
+       /* Maintain a reference so cx88-blackbird can query the 8800 device. */
+       core->v4ldev = dev;
+
        /* initial device configuration */
        mutex_lock(&core->lock);
        cx88_set_tvnorm(core, core->tvnorm);
        free_irq(pci_dev->irq, dev);
        mutex_unlock(&core->lock);
 fail_core:
+       core->v4ldev = NULL;
        cx88_core_put(core,dev->pci);
 fail_free:
        kfree(dev);
        free_irq(pci_dev->irq, dev);
        cx8800_unregister_video(dev);
 
+       core->v4ldev = NULL;
+
        /* free memory */
        cx88_core_put(core,dev->pci);
        kfree(dev);
 
        u32                    count;
 };
 
+struct cx8800_dev;
+struct cx8802_dev;
+
 struct cx88_core {
        struct list_head           devlist;
        atomic_t                   refcount;
        /* various v4l controls */
        u32                        freq;
 
-       /* cx88-video needs to access cx8802 for hybrid tuner pll access. */
+       /*
+        * cx88-video needs to access cx8802 for hybrid tuner pll access and
+        * for vb2_is_busy() checks.
+        */
        struct cx8802_dev          *dvbdev;
+       /* cx88-blackbird needs to access cx8800 for vb2_is_busy() checks */
+       struct cx8800_dev          *v4ldev;
        enum cx88_board_type       active_type_id;
        int                        active_ref;
        int                        active_fe_id;
                val;                                                            \
        })
 
-struct cx8800_dev;
-struct cx8802_dev;
-
 /* ----------------------------------------------------------- */
 /* function 0: video stuff                                     */