[PATCH v5 2/3] [media] media-device: split media initialization and registration

[Javier Martinez Canillas]

The media device node is registered and so made visible to user-space
before entities are registered and links created which means that the
media graph obtained by user-space could be only partially enumerated
if that happens too early before all the graph has been created.

To avoid this race condition, split the media init and registration
in separate functions and only register the media device node when
all the pending subdevices have been registered, either explicitly
by the driver or asynchronously using v4l2_async_register_subdev().

The media_device_register() had a check for drivers not filling dev
and model fields but all drivers in mainline set them and not doing
it will be a driver bug so change the function return to void and
add a BUG_ON() for dev being NULL instead.

Also, add a media_device_cleanup() function that will destroy the
graph_mutex that is initialized in media_device_init().

Suggested-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
Signed-off-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx>
Acked-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>

---

Changes in v5:
- Add kernel-doc for media_device_init() and media_device_register().

Changes in v4:
- Remove the model check from BUG_ON() since shold not be fatal.
  Suggested by Sakari Ailus.

Changes in v3:
- Replace the WARN_ON() in media_device_init() for a BUG_ON().
  Suggested by Sakari Ailus.

Changes in v2:
- Reword the documentation for media_device_unregister(). Suggested by Sakari.
- Added Sakari's Acked-by tag for patch #1.
- Change media_device_init() to return void instead of an error.
  Suggested by Sakari Ailus.
- Remove the error messages when media_device_register() fails.
  Suggested by Sakari Ailus.
- Fix typos in commit message of patch #2. Suggested by Sakari Ailus.

 drivers/media/common/siano/smsdvb-main.c      |  1 +
 drivers/media/media-device.c                  | 36 ++++++++++++++++++++++-----
 drivers/media/platform/exynos4-is/media-dev.c | 15 ++++++-----
 drivers/media/platform/omap3isp/isp.c         | 14 +++++------
 drivers/media/platform/s3c-camif/camif-core.c | 15 +++++++----
 drivers/media/platform/vsp1/vsp1_drv.c        | 12 ++++-----
 drivers/media/platform/xilinx/xilinx-vipp.c   | 12 +++------
 drivers/media/usb/au0828/au0828-core.c        | 27 ++++++++++----------
 drivers/media/usb/cx231xx/cx231xx-cards.c     | 30 +++++++++++-----------
 drivers/media/usb/dvb-usb-v2/dvb_usb_core.c   | 23 +++++++++--------
 drivers/media/usb/dvb-usb/dvb-usb-dvb.c       | 24 ++++++++++--------
 drivers/media/usb/siano/smsusb.c              |  5 ++--
 drivers/media/usb/uvc/uvc_driver.c            | 10 +++++---
 include/media/media-device.h                  | 26 +++++++++++++++++++
 14 files changed, 155 insertions(+), 95 deletions(-)

diff --git a/drivers/media/common/siano/smsdvb-main.c b/drivers/media/common/siano/smsdvb-main.c
index ab345490a43a..8a1ea2192439 100644
--- a/drivers/media/common/siano/smsdvb-main.c
+++ b/drivers/media/common/siano/smsdvb-main.c
@@ -617,6 +617,7 @@ static void smsdvb_media_device_unregister(struct smsdvb_client_t *client)
 	if (!coredev->media_dev)
 		return;
 	media_device_unregister(coredev->media_dev);
+	media_device_cleanup(coredev->media_dev);
 	kfree(coredev->media_dev);
 	coredev->media_dev = NULL;
 #endif
diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
index 11c1c7383361..5d5c8a57e7ba 100644
--- a/drivers/media/media-device.c
+++ b/drivers/media/media-device.c
@@ -529,7 +529,7 @@ static void media_device_release(struct media_devnode *mdev)
 }
 
 /**
- * media_device_register - register a media device
+ * media_device_init() - initialize a media device
  * @mdev:	The media device
  *
  * The caller is responsible for initializing the media device before
@@ -538,13 +538,10 @@ static void media_device_release(struct media_devnode *mdev)
  * - dev must point to the parent device
  * - model must be filled with the device model name
  */
-int __must_check __media_device_register(struct media_device *mdev,
-					 struct module *owner)
+void media_device_init(struct media_device *mdev)
 {
-	int ret;
 
-	if (WARN_ON(mdev->dev == NULL || mdev->model[0] == 0))
-		return -EINVAL;
+	BUG_ON(mdev->dev == NULL);
 
 	INIT_LIST_HEAD(&mdev->entities);
 	INIT_LIST_HEAD(&mdev->interfaces);
@@ -553,6 +550,33 @@ int __must_check __media_device_register(struct media_device *mdev,
 	spin_lock_init(&mdev->lock);
 	mutex_init(&mdev->graph_mutex);
 
+	dev_dbg(mdev->dev, "Media device initialized\n");
+}
+EXPORT_SYMBOL_GPL(media_device_init);
+
+/**
+ * media_device_cleanup() - Cleanup a media device
+ * @mdev:	The media device
+ *
+ */
+void media_device_cleanup(struct media_device *mdev)
+{
+	mutex_destroy(&mdev->graph_mutex);
+}
+EXPORT_SYMBOL_GPL(media_device_cleanup);
+
+/**
+ * __media_device_register() - register a media device
+ * @mdev:	The media device
+ * @owner:	The module owner
+ *
+ * returns zero on success or a negative error code.
+ */
+int __must_check __media_device_register(struct media_device *mdev,
+					 struct module *owner)
+{
+	int ret;
+
 	/* Register the device node. */
 	mdev->devnode.fops = &media_device_fops;
 	mdev->devnode.parent = mdev->dev;
diff --git a/drivers/media/platform/exynos4-is/media-dev.c b/drivers/media/platform/exynos4-is/media-dev.c
index a61ecedc1201..27663dd45294 100644
--- a/drivers/media/platform/exynos4-is/media-dev.c
+++ b/drivers/media/platform/exynos4-is/media-dev.c
@@ -1313,7 +1313,10 @@ static int subdev_notifier_complete(struct v4l2_async_notifier *notifier)
 	ret = v4l2_device_register_subdev_nodes(&fmd->v4l2_dev);
 unlock:
 	mutex_unlock(&fmd->media_dev.graph_mutex);
-	return ret;
+	if (ret < 0)
+		return ret;
+
+	return media_device_register(&fmd->media_dev);
 }
 
 static int fimc_md_probe(struct platform_device *pdev)
@@ -1350,11 +1353,7 @@ static int fimc_md_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	ret = media_device_register(&fmd->media_dev);
-	if (ret < 0) {
-		v4l2_err(v4l2_dev, "Failed to register media device: %d\n", ret);
-		goto err_v4l2_dev;
-	}
+	media_device_init(&fmd->media_dev);
 
 	ret = fimc_md_get_clocks(fmd);
 	if (ret)
@@ -1424,8 +1423,7 @@ err_clk:
 err_m_ent:
 	fimc_md_unregister_entities(fmd);
 err_md:
-	media_device_unregister(&fmd->media_dev);
-err_v4l2_dev:
+	media_device_cleanup(&fmd->media_dev);
 	v4l2_device_unregister(&fmd->v4l2_dev);
 	return ret;
 }
@@ -1445,6 +1443,7 @@ static int fimc_md_remove(struct platform_device *pdev)
 	fimc_md_unregister_entities(fmd);
 	fimc_md_pipelines_free(fmd);
 	media_device_unregister(&fmd->media_dev);
+	media_device_cleanup(&fmd->media_dev);
 	fimc_md_put_clocks(fmd);
 
 	return 0;
diff --git a/drivers/media/platform/omap3isp/isp.c b/drivers/media/platform/omap3isp/isp.c
index a4820bc07ec8..1f52d261c9c8 100644
--- a/drivers/media/platform/omap3isp/isp.c
+++ b/drivers/media/platform/omap3isp/isp.c
@@ -1793,6 +1793,7 @@ static void isp_unregister_entities(struct isp_device *isp)
 
 	v4l2_device_unregister(&isp->v4l2_dev);
 	media_device_unregister(&isp->media_dev);
+	media_device_cleanup(&isp->media_dev);
 }
 
 static int isp_link_entity(
@@ -1875,12 +1876,7 @@ static int isp_register_entities(struct isp_device *isp)
 		sizeof(isp->media_dev.model));
 	isp->media_dev.hw_revision = isp->revision;
 	isp->media_dev.link_notify = isp_pipeline_link_notify;
-	ret = media_device_register(&isp->media_dev);
-	if (ret < 0) {
-		dev_err(isp->dev, "%s: Media device registration failed (%d)\n",
-			__func__, ret);
-		return ret;
-	}
+	media_device_init(&isp->media_dev);
 
 	isp->v4l2_dev.mdev = &isp->media_dev;
 	ret = v4l2_device_register(isp->dev, &isp->v4l2_dev);
@@ -2365,7 +2361,11 @@ static int isp_subdev_notifier_complete(struct v4l2_async_notifier *async)
 		}
 	}
 
-	return v4l2_device_register_subdev_nodes(v4l2_dev);
+	ret = v4l2_device_register_subdev_nodes(&isp->v4l2_dev);
+	if (ret < 0)
+		return ret;
+
+	return media_device_register(&isp->media_dev);
 }
 
 /*
diff --git a/drivers/media/platform/s3c-camif/camif-core.c b/drivers/media/platform/s3c-camif/camif-core.c
index 8649d4c0e90d..ea02b7ef2119 100644
--- a/drivers/media/platform/s3c-camif/camif-core.c
+++ b/drivers/media/platform/s3c-camif/camif-core.c
@@ -305,7 +305,7 @@ static void camif_unregister_media_entities(struct camif_dev *camif)
 /*
  * Media device
  */
-static int camif_media_dev_register(struct camif_dev *camif)
+static int camif_media_dev_init(struct camif_dev *camif)
 {
 	struct media_device *md = &camif->media_dev;
 	struct v4l2_device *v4l2_dev = &camif->v4l2_dev;
@@ -328,9 +328,7 @@ static int camif_media_dev_register(struct camif_dev *camif)
 	if (ret < 0)
 		return ret;
 
-	ret = media_device_register(md);
-	if (ret < 0)
-		v4l2_device_unregister(v4l2_dev);
+	media_device_init(md);
 
 	return ret;
 }
@@ -483,7 +481,7 @@ static int s3c_camif_probe(struct platform_device *pdev)
 		goto err_alloc;
 	}
 
-	ret = camif_media_dev_register(camif);
+	ret = camif_media_dev_init(camif);
 	if (ret < 0)
 		goto err_mdev;
 
@@ -510,6 +508,11 @@ static int s3c_camif_probe(struct platform_device *pdev)
 		goto err_unlock;
 
 	mutex_unlock(&camif->media_dev.graph_mutex);
+
+	ret = media_device_register(&camif->media_dev);
+	if (ret < 0)
+		goto err_sens;
+
 	pm_runtime_put(dev);
 	return 0;
 
@@ -518,6 +521,7 @@ err_unlock:
 err_sens:
 	v4l2_device_unregister(&camif->v4l2_dev);
 	media_device_unregister(&camif->media_dev);
+	media_device_cleanup(&camif->media_dev);
 	camif_unregister_media_entities(camif);
 err_mdev:
 	vb2_dma_contig_cleanup_ctx(camif->alloc_ctx);
@@ -539,6 +543,7 @@ static int s3c_camif_remove(struct platform_device *pdev)
 	struct s3c_camif_plat_data *pdata = &camif->pdata;
 
 	media_device_unregister(&camif->media_dev);
+	media_device_cleanup(&camif->media_dev);
 	camif_unregister_media_entities(camif);
 	v4l2_device_unregister(&camif->v4l2_dev);
 
diff --git a/drivers/media/platform/vsp1/vsp1_drv.c b/drivers/media/platform/vsp1/vsp1_drv.c
index 0b251147bfff..42dff9d020af 100644
--- a/drivers/media/platform/vsp1/vsp1_drv.c
+++ b/drivers/media/platform/vsp1/vsp1_drv.c
@@ -127,6 +127,7 @@ static void vsp1_destroy_entities(struct vsp1_device *vsp1)
 
 	v4l2_device_unregister(&vsp1->v4l2_dev);
 	media_device_unregister(&vsp1->media_dev);
+	media_device_cleanup(&vsp1->media_dev);
 }
 
 static int vsp1_create_entities(struct vsp1_device *vsp1)
@@ -141,12 +142,7 @@ static int vsp1_create_entities(struct vsp1_device *vsp1)
 	strlcpy(mdev->model, "VSP1", sizeof(mdev->model));
 	snprintf(mdev->bus_info, sizeof(mdev->bus_info), "platform:%s",
 		 dev_name(mdev->dev));
-	ret = media_device_register(mdev);
-	if (ret < 0) {
-		dev_err(vsp1->dev, "media device registration failed (%d)\n",
-			ret);
-		return ret;
-	}
+	media_device_init(mdev);
 
 	vdev->mdev = mdev;
 	ret = v4l2_device_register(vsp1->dev, vdev);
@@ -284,6 +280,10 @@ static int vsp1_create_entities(struct vsp1_device *vsp1)
 	}
 
 	ret = v4l2_device_register_subdev_nodes(&vsp1->v4l2_dev);
+	if (ret < 0)
+		goto done;
+
+	ret = media_device_register(mdev);
 
 done:
 	if (ret < 0)
diff --git a/drivers/media/platform/xilinx/xilinx-vipp.c b/drivers/media/platform/xilinx/xilinx-vipp.c
index 2352f7e5a6a3..e795a4501e8b 100644
--- a/drivers/media/platform/xilinx/xilinx-vipp.c
+++ b/drivers/media/platform/xilinx/xilinx-vipp.c
@@ -311,7 +311,7 @@ static int xvip_graph_notify_complete(struct v4l2_async_notifier *notifier)
 	if (ret < 0)
 		dev_err(xdev->dev, "failed to register subdev nodes\n");
 
-	return ret;
+	return media_device_register(&xdev->media_dev);
 }
 
 static int xvip_graph_notify_bound(struct v4l2_async_notifier *notifier,
@@ -573,6 +573,7 @@ static void xvip_composite_v4l2_cleanup(struct xvip_composite_device *xdev)
 {
 	v4l2_device_unregister(&xdev->v4l2_dev);
 	media_device_unregister(&xdev->media_dev);
+	media_device_cleanup(&xdev->media_dev);
 }
 
 static int xvip_composite_v4l2_init(struct xvip_composite_device *xdev)
@@ -584,19 +585,14 @@ static int xvip_composite_v4l2_init(struct xvip_composite_device *xdev)
 		sizeof(xdev->media_dev.model));
 	xdev->media_dev.hw_revision = 0;
 
-	ret = media_device_register(&xdev->media_dev);
-	if (ret < 0) {
-		dev_err(xdev->dev, "media device registration failed (%d)\n",
-			ret);
-		return ret;
-	}
+	media_device_init(&xdev->media_dev);
 
 	xdev->v4l2_dev.mdev = &xdev->media_dev;
 	ret = v4l2_device_register(xdev->dev, &xdev->v4l2_dev);
 	if (ret < 0) {
 		dev_err(xdev->dev, "V4L2 device registration failed (%d)\n",
 			ret);
-		media_device_unregister(&xdev->media_dev);
+		media_device_cleanup(&xdev->media_dev);
 		return ret;
 	}
 
diff --git a/drivers/media/usb/au0828/au0828-core.c b/drivers/media/usb/au0828/au0828-core.c
index 1b207fa16a55..e7aab47ae4f5 100644
--- a/drivers/media/usb/au0828/au0828-core.c
+++ b/drivers/media/usb/au0828/au0828-core.c
@@ -136,6 +136,7 @@ static void au0828_unregister_media_device(struct au0828_dev *dev)
 #ifdef CONFIG_MEDIA_CONTROLLER
 	if (dev->media_dev) {
 		media_device_unregister(dev->media_dev);
+		media_device_cleanup(dev->media_dev);
 		kfree(dev->media_dev);
 		dev->media_dev = NULL;
 	}
@@ -216,12 +217,11 @@ static void au0828_usb_disconnect(struct usb_interface *interface)
 	au0828_usb_release(dev);
 }
 
-static void au0828_media_device_register(struct au0828_dev *dev,
-					  struct usb_device *udev)
+static void au0828_media_device_init(struct au0828_dev *dev,
+				     struct usb_device *udev)
 {
 #ifdef CONFIG_MEDIA_CONTROLLER
 	struct media_device *mdev;
-	int ret;
 
 	mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
 	if (!mdev)
@@ -239,14 +239,7 @@ static void au0828_media_device_register(struct au0828_dev *dev,
 	mdev->hw_revision = le16_to_cpu(udev->descriptor.bcdDevice);
 	mdev->driver_version = LINUX_VERSION_CODE;
 
-	ret = media_device_register(mdev);
-	if (ret) {
-		pr_err(
-			"Couldn't create a media device. Error: %d\n",
-			ret);
-		kfree(mdev);
-		return;
-	}
+	media_device_init(mdev);
 
 	dev->media_dev = mdev;
 #endif
@@ -374,8 +367,8 @@ static int au0828_usb_probe(struct usb_interface *interface,
 	dev->boardnr = id->driver_info;
 	dev->board = au0828_boards[dev->boardnr];
 
-	/* Register the media controller */
-	au0828_media_device_register(dev, usbdev);
+	/* Initialize the media controller */
+	au0828_media_device_init(dev, usbdev);
 
 #ifdef CONFIG_VIDEO_AU0828_V4L2
 	dev->v4l2_dev.release = au0828_usb_v4l2_release;
@@ -446,9 +439,15 @@ static int au0828_usb_probe(struct usb_interface *interface,
 	if (retval) {
 		pr_err("%s() au0282_dev_register failed to create graph\n",
 		       __func__);
-		au0828_usb_disconnect(interface);
+		goto done;
 	}
 
+	retval = media_device_register(dev->media_dev);
+
+done:
+	if (retval < 0)
+		au0828_usb_disconnect(interface);
+
 	return retval;
 }
 
diff --git a/drivers/media/usb/cx231xx/cx231xx-cards.c b/drivers/media/usb/cx231xx/cx231xx-cards.c
index 0e1efc59ff58..2e997f09a4cd 100644
--- a/drivers/media/usb/cx231xx/cx231xx-cards.c
+++ b/drivers/media/usb/cx231xx/cx231xx-cards.c
@@ -1172,6 +1172,7 @@ static void cx231xx_unregister_media_device(struct cx231xx *dev)
 #ifdef CONFIG_MEDIA_CONTROLLER
 	if (dev->media_dev) {
 		media_device_unregister(dev->media_dev);
+		media_device_cleanup(dev->media_dev);
 		kfree(dev->media_dev);
 		dev->media_dev = NULL;
 	}
@@ -1205,12 +1206,11 @@ void cx231xx_release_resources(struct cx231xx *dev)
 	clear_bit(dev->devno, &cx231xx_devused);
 }
 
-static void cx231xx_media_device_register(struct cx231xx *dev,
-					  struct usb_device *udev)
+static void cx231xx_media_device_init(struct cx231xx *dev,
+				      struct usb_device *udev)
 {
 #ifdef CONFIG_MEDIA_CONTROLLER
 	struct media_device *mdev;
-	int ret;
 
 	mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
 	if (!mdev)
@@ -1224,14 +1224,7 @@ static void cx231xx_media_device_register(struct cx231xx *dev,
 	mdev->hw_revision = le16_to_cpu(udev->descriptor.bcdDevice);
 	mdev->driver_version = LINUX_VERSION_CODE;
 
-	ret = media_device_register(mdev);
-	if (ret) {
-		dev_err(dev->dev,
-			"Couldn't create a media device. Error: %d\n",
-			ret);
-		kfree(mdev);
-		return;
-	}
+	media_device_init(mdev);
 
 	dev->media_dev = mdev;
 #endif
@@ -1669,8 +1662,8 @@ static int cx231xx_usb_probe(struct usb_interface *interface,
 	/* save our data pointer in this interface device */
 	usb_set_intfdata(interface, dev);
 
-	/* Register the media controller */
-	cx231xx_media_device_register(dev, udev);
+	/* Initialize the media controller */
+	cx231xx_media_device_init(dev, udev);
 
 	/* Create v4l2 device */
 #ifdef CONFIG_MEDIA_CONTROLLER
@@ -1742,11 +1735,16 @@ static int cx231xx_usb_probe(struct usb_interface *interface,
 	request_modules(dev);
 
 	retval = cx231xx_create_media_graph(dev);
-	if (retval < 0) {
-		cx231xx_release_resources(dev);
-	}
+	if (retval < 0)
+		goto done;
+
+	retval = media_device_register(dev->media_dev);
 
+done:
+	if (retval < 0)
+		cx231xx_release_resources(dev);
 	return retval;
+
 err_video_alt:
 	/* cx231xx_uninit_dev: */
 	cx231xx_close_extension(dev);
diff --git a/drivers/media/usb/dvb-usb-v2/dvb_usb_core.c b/drivers/media/usb/dvb-usb-v2/dvb_usb_core.c
index 6d3f61f6dc77..a0413dcc3361 100644
--- a/drivers/media/usb/dvb-usb-v2/dvb_usb_core.c
+++ b/drivers/media/usb/dvb-usb-v2/dvb_usb_core.c
@@ -400,7 +400,7 @@ skip_feed_stop:
 	return ret;
 }
 
-static void dvb_usbv2_media_device_register(struct dvb_usb_adapter *adap)
+static void dvb_usbv2_media_device_init(struct dvb_usb_adapter *adap)
 {
 #ifdef CONFIG_MEDIA_CONTROLLER_DVB
 	struct media_device *mdev;
@@ -420,14 +420,7 @@ static void dvb_usbv2_media_device_register(struct dvb_usb_adapter *adap)
 	mdev->hw_revision = le16_to_cpu(udev->descriptor.bcdDevice);
 	mdev->driver_version = LINUX_VERSION_CODE;
 
-	ret = media_device_register(mdev);
-	if (ret) {
-		dev_err(&d->udev->dev,
-			"Couldn't create a media device. Error: %d\n",
-			ret);
-		kfree(mdev);
-		return;
-	}
+	media_device_init(mdev);
 
 	dvb_register_media_controller(&adap->dvb_adap, mdev);
 
@@ -436,6 +429,13 @@ static void dvb_usbv2_media_device_register(struct dvb_usb_adapter *adap)
 #endif
 }
 
+static void dvb_usbv2_media_device_register(struct dvb_usb_adapter *adap)
+{
+#ifdef CONFIG_MEDIA_CONTROLLER_DVB
+	media_device_register(adap->dvb_adap.mdev);
+#endif
+}
+
 static void dvb_usbv2_media_device_unregister(struct dvb_usb_adapter *adap)
 {
 #ifdef CONFIG_MEDIA_CONTROLLER_DVB
@@ -444,6 +444,7 @@ static void dvb_usbv2_media_device_unregister(struct dvb_usb_adapter *adap)
 		return;
 
 	media_device_unregister(adap->dvb_adap.mdev);
+	media_device_cleanup(adap->dvb_adap.mdev);
 	kfree(adap->dvb_adap.mdev);
 	adap->dvb_adap.mdev = NULL;
 
@@ -467,7 +468,7 @@ static int dvb_usbv2_adapter_dvb_init(struct dvb_usb_adapter *adap)
 
 	adap->dvb_adap.priv = adap;
 
-	dvb_usbv2_media_device_register(adap);
+	dvb_usbv2_media_device_init(adap);
 
 	if (d->props->read_mac_address) {
 		ret = d->props->read_mac_address(adap,
@@ -702,6 +703,8 @@ static int dvb_usbv2_adapter_frontend_init(struct dvb_usb_adapter *adap)
 	if (ret < 0)
 		goto err_dvb_unregister_frontend;
 
+	dvb_usbv2_media_device_register(&adap->dvb_adap);
+
 	return 0;
 
 err_dvb_unregister_frontend:
diff --git a/drivers/media/usb/dvb-usb/dvb-usb-dvb.c b/drivers/media/usb/dvb-usb/dvb-usb-dvb.c
index b51dbdf03f42..4086d9626664 100644
--- a/drivers/media/usb/dvb-usb/dvb-usb-dvb.c
+++ b/drivers/media/usb/dvb-usb/dvb-usb-dvb.c
@@ -95,7 +95,7 @@ static int dvb_usb_stop_feed(struct dvb_demux_feed *dvbdmxfeed)
 	return dvb_usb_ctrl_feed(dvbdmxfeed, 0);
 }
 
-static void dvb_usb_media_device_register(struct dvb_usb_adapter *adap)
+static void dvb_usb_media_device_init(struct dvb_usb_adapter *adap)
 {
 #ifdef CONFIG_MEDIA_CONTROLLER_DVB
 	struct media_device *mdev;
@@ -115,20 +115,21 @@ static void dvb_usb_media_device_register(struct dvb_usb_adapter *adap)
 	mdev->hw_revision = le16_to_cpu(udev->descriptor.bcdDevice);
 	mdev->driver_version = LINUX_VERSION_CODE;
 
-	ret = media_device_register(mdev);
-	if (ret) {
-		dev_err(&d->udev->dev,
-			"Couldn't create a media device. Error: %d\n",
-			ret);
-		kfree(mdev);
-		return;
-	}
+	media_device_init(mdev);
+
 	dvb_register_media_controller(&adap->dvb_adap, mdev);
 
 	dev_info(&d->udev->dev, "media controller created\n");
 #endif
 }
 
+static void dvb_usb_media_device_register(struct dvb_usb_adapter *adap)
+{
+#ifdef CONFIG_MEDIA_CONTROLLER_DVB
+	media_device_register(adap->dvb_adap.mdev);
+#endif
+}
+
 static void dvb_usb_media_device_unregister(struct dvb_usb_adapter *adap)
 {
 #ifdef CONFIG_MEDIA_CONTROLLER_DVB
@@ -136,6 +137,7 @@ static void dvb_usb_media_device_unregister(struct dvb_usb_adapter *adap)
 		return;
 
 	media_device_unregister(adap->dvb_adap.mdev);
+	media_device_cleanup(adap->dvb_adap.mdev);
 	kfree(adap->dvb_adap.mdev);
 	adap->dvb_adap.mdev = NULL;
 #endif
@@ -154,7 +156,7 @@ int dvb_usb_adapter_dvb_init(struct dvb_usb_adapter *adap, short *adapter_nums)
 	}
 	adap->dvb_adap.priv = adap;
 
-	dvb_usb_media_device_register(adap);
+	dvb_usb_media_device_init(adap);
 
 	if (adap->dev->props.read_mac_address) {
 		if (adap->dev->props.read_mac_address(adap->dev, adap->dvb_adap.proposed_mac) == 0)
@@ -323,6 +325,8 @@ int dvb_usb_adapter_frontend_init(struct dvb_usb_adapter *adap)
 
 	ret = dvb_create_media_graph(&adap->dvb_adap);
 
+	dvb_usb_media_device_register(adap);
+
 	return ret;
 }
 
diff --git a/drivers/media/usb/siano/smsusb.c b/drivers/media/usb/siano/smsusb.c
index c945e4c2fbd4..8abbd3cc8eba 100644
--- a/drivers/media/usb/siano/smsusb.c
+++ b/drivers/media/usb/siano/smsusb.c
@@ -361,10 +361,11 @@ static void *siano_media_device_register(struct smsusb_device_t *dev,
 	mdev->hw_revision = le16_to_cpu(udev->descriptor.bcdDevice);
 	mdev->driver_version = LINUX_VERSION_CODE;
 
+	media_device_init(mdev);
+
 	ret = media_device_register(mdev);
 	if (ret) {
-		pr_err("Couldn't create a media device. Error: %d\n",
-			ret);
+		media_device_cleanup(mdev);
 		kfree(mdev);
 		return NULL;
 	}
diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 922665b59d38..f3ee4c248b2f 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -1676,6 +1676,7 @@ static void uvc_delete(struct uvc_device *dev)
 #ifdef CONFIG_MEDIA_CONTROLLER
 	if (media_devnode_is_registered(&dev->mdev.devnode))
 		media_device_unregister(&dev->mdev);
+	media_device_cleanup(&dev->mdev);
 #endif
 
 	list_for_each_safe(p, n, &dev->chains) {
@@ -1926,7 +1927,7 @@ static int uvc_probe(struct usb_interface *intf,
 			"linux-uvc-devel mailing list.\n");
 	}
 
-	/* Register the media and V4L2 devices. */
+	/* Initialize the media device and register the V4L2 device. */
 #ifdef CONFIG_MEDIA_CONTROLLER
 	dev->mdev.dev = &intf->dev;
 	strlcpy(dev->mdev.model, dev->name, sizeof(dev->mdev.model));
@@ -1936,8 +1937,7 @@ static int uvc_probe(struct usb_interface *intf,
 	strcpy(dev->mdev.bus_info, udev->devpath);
 	dev->mdev.hw_revision = le16_to_cpu(udev->descriptor.bcdDevice);
 	dev->mdev.driver_version = LINUX_VERSION_CODE;
-	if (media_device_register(&dev->mdev) < 0)
-		goto error;
+	media_device_init(&dev->mdev);
 
 	dev->vdev.mdev = &dev->mdev;
 #endif
@@ -1956,6 +1956,10 @@ static int uvc_probe(struct usb_interface *intf,
 	if (uvc_register_chains(dev) < 0)
 		goto error;
 
+	/* Register the media device node */
+	if (media_device_register(&dev->mdev) < 0)
+		goto error;
+
 	/* Save our data pointer in the interface data. */
 	usb_set_intfdata(intf, dev);
 
diff --git a/include/media/media-device.h b/include/media/media-device.h
index b0594be5d631..afdc35fbf69a 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -338,6 +338,32 @@ struct media_device {
 #define to_media_device(node) container_of(node, struct media_device, devnode)
 
 /**
+ * media_device_init() - Initializes a media device element
+ *
+ * @mdev:	pointer to struct &media_device
+ *
+ * This function initializes the media device prior to its registration.
+ * The media device initialization and registration is split in two functions
+ * to avoid race conditions and make the media device available to user-space
+ * before the media graph has been completed.
+ *
+ * So drivers need to first initialize the media device, register any entity
+ * within the media device, create pad to pad links and then finally register
+ * the media device by calling media_device_register() as a final step. 
+ */
+void media_device_init(struct media_device *mdev);
+
+/**
+ * media_device_cleanup() - Cleanups a media device element
+ *
+ * @mdev:	pointer to struct &media_device
+ *
+ * This function that will destroy the graph_mutex that is
+ * initialized in media_device_init().
+ */
+void media_device_cleanup(struct media_device *mdev);
+
+/**
  * __media_device_register() - Registers a media device element
  *
  * @mdev:	pointer to struct &media_device
-- 
2.4.3

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