Re: [PATCH 2/8] vfio/mdev: embedd struct mdev_parent in the parent data structure

[Kirti Wankhede <kwankhede@nvidia.com>]

On 6/3/2022 12:03 PM, Christoph Hellwig wrote:
> Simplify mdev_{un}register_device by requiring the caller to pass in
> a structure allocate as part of the parent device structure.  This
> removes the need for a list of parents and the separate mdev_parent
> refcount as we can simplify rely on the reference to the parent device.
> 

By removing this list, there is no way to know if parent device is 
registered repeatedly? What will happen if same parent device is 
registered twice? will it fail somewhere else?

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   .../driver-api/vfio-mediated-device.rst       |  12 +-
>   Documentation/s390/vfio-ap.rst                |   2 +-
>   Documentation/s390/vfio-ccw.rst               |   2 +-
>   drivers/gpu/drm/i915/gvt/kvmgt.c              |   5 +-
>   drivers/gpu/drm/i915/i915_drv.h               |   2 +
>   drivers/s390/cio/cio.h                        |   2 +
>   drivers/s390/cio/vfio_ccw_ops.c               |   6 +-
>   drivers/s390/crypto/vfio_ap_ops.c             |   5 +-
>   drivers/s390/crypto/vfio_ap_private.h         |   1 +
>   drivers/vfio/mdev/mdev_core.c                 | 116 +++---------------
>   drivers/vfio/mdev/mdev_private.h              |  23 ----
>   drivers/vfio/mdev/mdev_sysfs.c                |   4 +-
>   include/linux/mdev.h                          |  15 ++-
>   samples/vfio-mdev/mbochs.c                    |   5 +-
>   samples/vfio-mdev/mdpy.c                      |   5 +-
>   samples/vfio-mdev/mtty.c                      |   6 +-
>   16 files changed, 65 insertions(+), 146 deletions(-)
> 
> diff --git a/Documentation/driver-api/vfio-mediated-device.rst b/Documentation/driver-api/vfio-mediated-device.rst
> index eded8719180fb..3749f59c855fa 100644
> --- a/Documentation/driver-api/vfio-mediated-device.rst
> +++ b/Documentation/driver-api/vfio-mediated-device.rst
> @@ -60,19 +60,19 @@ devices as examples, as these devices are the first devices to use this module::
>        |  MDEV CORE    |
>        |   MODULE      |
>        |   mdev.ko     |
> -     | +-----------+ |  mdev_register_device() +--------------+
> +     | +-----------+ |  mdev_register_parent() +--------------+
>        | |           | +<------------------------+              |
>        | |           | |                         |  nvidia.ko   |<-> physical
>        | |           | +------------------------>+              |    device
>        | |           | |        callbacks        +--------------+
>        | | Physical  | |
> -     | |  device   | |  mdev_register_device() +--------------+
> +     | |  device   | |  mdev_register_parent() +--------------+
>        | | interface | |<------------------------+              |
>        | |           | |                         |  i915.ko     |<-> physical
>        | |           | +------------------------>+              |    device
>        | |           | |        callbacks        +--------------+
>        | |           | |
> -     | |           | |  mdev_register_device() +--------------+
> +     | |           | |  mdev_register_parent() +--------------+
>        | |           | +<------------------------+              |
>        | |           | |                         | ccw_device.ko|<-> physical
>        | |           | +------------------------>+              |    device
> @@ -127,8 +127,8 @@ vfio_device_ops.
>   When a driver wants to add the GUID creation sysfs to an existing device it has
>   probe'd to then it should call::
>   
> -	extern int  mdev_register_device(struct device *dev,
> -	                                 struct mdev_driver *mdev_driver);
> +	int mdev_register_parent(struct mdev_parent *parent, struct device *dev,
> +			struct mdev_driver *mdev_driver);
>

No need to change API name as it still registers 'struct device *dev', 
it could be 'mdev_register_device' but with new argument list.

>   This will provide the 'mdev_supported_types/XX/create' files which can then be
>   used to trigger the creation of a mdev_device. The created mdev_device will be
> @@ -136,7 +136,7 @@ attached to the specified driver.
>   
>   When the driver needs to remove itself it calls::
>   
> -	extern void mdev_unregister_device(struct device *dev);
> +	void mdev_unregister_parent(struct mdev_parent *parent);
>   

Same as above.

>   Which will unbind and destroy all the created mdevs and remove the sysfs files.
>   
> diff --git a/Documentation/s390/vfio-ap.rst b/Documentation/s390/vfio-ap.rst
> index f57ae621f33e8..37e16158c7fbf 100644
> --- a/Documentation/s390/vfio-ap.rst
> +++ b/Documentation/s390/vfio-ap.rst
> @@ -299,7 +299,7 @@ of the VFIO AP mediated matrix device driver::
>      |  MDEV CORE  |
>      |   MODULE    |
>      |   mdev.ko   |
> -   | +---------+ | mdev_register_device() +--------------+
> +   | +---------+ | mdev_register_parent() +--------------+
>      | |Physical | +<-----------------------+              |
>      | | device  | |                        |  vfio_ap.ko  |<-> matrix
>      | |interface| +----------------------->+              |    device
> diff --git a/Documentation/s390/vfio-ccw.rst b/Documentation/s390/vfio-ccw.rst
> index 8aad08a8b8a50..ea928a3806f43 100644
> --- a/Documentation/s390/vfio-ccw.rst
> +++ b/Documentation/s390/vfio-ccw.rst
> @@ -156,7 +156,7 @@ Below is a high Level block diagram::
>    |  MDEV CORE  |
>    |   MODULE    |
>    |   mdev.ko   |
> - | +---------+ | mdev_register_device() +--------------+
> + | +---------+ | mdev_register_parent() +--------------+
>    | |Physical | +<-----------------------+              |
>    | | device  | |                        |  vfio_ccw.ko |<-> subchannel
>    | |interface| +----------------------->+              |     device
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index e2f6c56ab3420..37bda01c1bb97 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -1960,7 +1960,7 @@ static void intel_gvt_clean_device(struct drm_i915_private *i915)
>   	if (drm_WARN_ON(&i915->drm, !gvt))
>   		return;
>   
> -	mdev_unregister_device(i915->drm.dev);
> +	mdev_unregister_parent(&i915->vgpu.parent);

Ideally, parent should be member of gvt. There could be multiple vgpus 
created on one physical device. Intel folks would be better reviewer though.

>   	intel_gvt_cleanup_vgpu_type_groups(gvt);
>   	intel_gvt_destroy_idle_vgpu(gvt->idle_vgpu);
>   	intel_gvt_clean_vgpu_types(gvt);
> @@ -2065,7 +2065,8 @@ static int intel_gvt_init_device(struct drm_i915_private *i915)
>   	if (ret)
>   		goto out_destroy_idle_vgpu;
>   
> -	ret = mdev_register_device(i915->drm.dev, &intel_vgpu_mdev_driver);
> +	ret = mdev_register_parent(&i915->vgpu.parent, i915->drm.dev,
> +				   &intel_vgpu_mdev_driver);
>   	if (ret)
>   		goto out_cleanup_vgpu_type_groups;
>   
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 00d7eeae33bd3..7d62cc9a57e4e 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -32,6 +32,7 @@
>   
>   #include <uapi/drm/i915_drm.h>
>   
> +#include <linux/mdev.h>
>   #include <linux/pm_qos.h>
>   
>   #include <drm/drm_connector.h>
> @@ -400,6 +401,7 @@ struct i915_frontbuffer_tracking {
>   
>   struct i915_virtual_gpu {
>   	struct mutex lock; /* serialises sending of g2v_notify command pkts */
> +	struct mdev_parent parent;
>   	bool active;
>   	u32 caps;
>   	u32 *initial_mmio;
> diff --git a/drivers/s390/cio/cio.h b/drivers/s390/cio/cio.h
> index 1cb9daf9c6450..4ae462da7b45b 100644
> --- a/drivers/s390/cio/cio.h
> +++ b/drivers/s390/cio/cio.h
> @@ -5,6 +5,7 @@
>   #include <linux/mutex.h>
>   #include <linux/device.h>
>   #include <linux/mod_devicetable.h>
> +#include <linux/mdev.h>
>   #include <asm/chpid.h>
>   #include <asm/cio.h>
>   #include <asm/fcx.h>
> @@ -104,6 +105,7 @@ struct subchannel {
>   	struct schib_config config;
>   	u64 dma_mask;
>   	char *driver_override; /* Driver name to force a match */
> +	struct mdev_parent parent;
>   } __attribute__ ((aligned(8)));
>   
>   DECLARE_PER_CPU_ALIGNED(struct irb, cio_irb);
> diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
> index b49e2e9db2dc6..9192a21085ce4 100644
> --- a/drivers/s390/cio/vfio_ccw_ops.c
> +++ b/drivers/s390/cio/vfio_ccw_ops.c
> @@ -11,7 +11,6 @@
>    */
>   
>   #include <linux/vfio.h>
> -#include <linux/mdev.h>
>   #include <linux/nospec.h>
>   #include <linux/slab.h>
>   
> @@ -660,10 +659,11 @@ struct mdev_driver vfio_ccw_mdev_driver = {
>   
>   int vfio_ccw_mdev_reg(struct subchannel *sch)
>   {
> -	return mdev_register_device(&sch->dev, &vfio_ccw_mdev_driver);
> +	return mdev_register_parent(&sch->parent, &sch->dev,
> +				    &vfio_ccw_mdev_driver);
>   }
>   
>   void vfio_ccw_mdev_unreg(struct subchannel *sch)
>   {
> -	mdev_unregister_device(&sch->dev);
> +	mdev_unregister_parent(&sch->parent);
>   }
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index a7d2a95796d36..834945150dc9f 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -1485,7 +1485,8 @@ int vfio_ap_mdev_register(void)
>   	if (ret)
>   		return ret;
>   
> -	ret = mdev_register_device(&matrix_dev->device, &vfio_ap_matrix_driver);
> +	ret = mdev_register_parent(&matrix_dev->parent, &matrix_dev->device,
> +				   &vfio_ap_matrix_driver);
>   	if (ret)
>   		goto err_driver;
>   	return 0;
> @@ -1497,6 +1498,6 @@ int vfio_ap_mdev_register(void)
>   
>   void vfio_ap_mdev_unregister(void)
>   {
> -	mdev_unregister_device(&matrix_dev->device);
> +	mdev_unregister_parent(&matrix_dev->parent);
>   	mdev_unregister_driver(&vfio_ap_matrix_driver);
>   }
> diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
> index a26efd804d0df..b97dc548a7c95 100644
> --- a/drivers/s390/crypto/vfio_ap_private.h
> +++ b/drivers/s390/crypto/vfio_ap_private.h
> @@ -46,6 +46,7 @@ struct ap_matrix_dev {
>   	struct list_head mdev_list;
>   	struct mutex lock;
>   	struct ap_driver  *vfio_ap_drv;
> +	struct mdev_parent parent;
>   };
>   
>   extern struct ap_matrix_dev *matrix_dev;
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index b8b9e7911e559..8b5a2b3f0c882 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -20,8 +20,6 @@
>   #define DRIVER_AUTHOR		"NVIDIA Corporation"
>   #define DRIVER_DESC		"Mediated device Core Driver"
>   
> -static LIST_HEAD(parent_list);
> -static DEFINE_MUTEX(parent_list_lock);
>   static struct class_compat *mdev_bus_compat_class;
>   
>   static LIST_HEAD(mdev_list);
> @@ -63,28 +61,6 @@ struct device *mtype_get_parent_dev(struct mdev_type *mtype)
>   }
>   EXPORT_SYMBOL(mtype_get_parent_dev);
>   
> -/* Should be called holding parent_list_lock */
> -static struct mdev_parent *__find_parent_device(struct device *dev)
> -{
> -	struct mdev_parent *parent;
> -
> -	list_for_each_entry(parent, &parent_list, next) {
> -		if (parent->dev == dev)
> -			return parent;
> -	}
> -	return NULL;
> -}
> -
> -void mdev_release_parent(struct kref *kref)
> -{
> -	struct mdev_parent *parent = container_of(kref, struct mdev_parent,
> -						  ref);
> -	struct device *dev = parent->dev;
> -
> -	kfree(parent);
> -	put_device(dev);
> -}
> -
>   /* Caller must hold parent unreg_sem read or write lock */
>   static void mdev_device_remove_common(struct mdev_device *mdev)
>   {
> @@ -107,125 +83,69 @@ static int mdev_device_remove_cb(struct device *dev, void *data)
>   }
>   
>   /*
> - * mdev_register_device : Register a device
> + * mdev_register_parent: Register a device as parent for mdevs
> + * @parent: parent structure registered
>    * @dev: device structure representing parent device.
>    * @mdev_driver: Device driver to bind to the newly created mdev
>    *
> - * Add device to list of registered parent devices.
>    * Returns a negative value on error, otherwise 0.
>    */
> -int mdev_register_device(struct device *dev, struct mdev_driver *mdev_driver)
> +int mdev_register_parent(struct mdev_parent *parent, struct device *dev,
> +		struct mdev_driver *mdev_driver)
>   {
> -	int ret;
> -	struct mdev_parent *parent;
>   	char *env_string = "MDEV_STATE=registered";
>   	char *envp[] = { env_string, NULL };
> +	int ret;
>   
>   	/* check for mandatory ops */
>   	if (!mdev_driver->supported_type_groups)
>   		return -EINVAL;
>   
> -	dev = get_device(dev);
> -	if (!dev)
> -		return -EINVAL;
> -

Why not held device here? What if some driver miss behave where it 
registers device to mdev, but unloads without unregistering from mdev?

Thanks,
Kirti

> -	mutex_lock(&parent_list_lock);
> -
> -	/* Check for duplicate */
> -	parent = __find_parent_device(dev);
> -	if (parent) {
> -		parent = NULL;
> -		ret = -EEXIST;
> -		goto add_dev_err;
> -	}
> -
> -	parent = kzalloc(sizeof(*parent), GFP_KERNEL);
> -	if (!parent) {
> -		ret = -ENOMEM;
> -		goto add_dev_err;
> -	}
> -
> -	kref_init(&parent->ref);
> +	memset(parent, 0, sizeof(*parent));
>   	init_rwsem(&parent->unreg_sem);
> -
>   	parent->dev = dev;
>   	parent->mdev_driver = mdev_driver;
>   
>   	if (!mdev_bus_compat_class) {
>   		mdev_bus_compat_class = class_compat_register("mdev_bus");
> -		if (!mdev_bus_compat_class) {
> -			ret = -ENOMEM;
> -			goto add_dev_err;
> -		}
> +		if (!mdev_bus_compat_class)
> +			return -ENOMEM;
>   	}
>   
>   	ret = parent_create_sysfs_files(parent);
>   	if (ret)
> -		goto add_dev_err;
> +		return ret;
>   
>   	ret = class_compat_create_link(mdev_bus_compat_class, dev, NULL);
>   	if (ret)
>   		dev_warn(dev, "Failed to create compatibility class link\n");
>   
> -	list_add(&parent->next, &parent_list);
> -	mutex_unlock(&parent_list_lock);
> -
>   	dev_info(dev, "MDEV: Registered\n");
>   	kobject_uevent_env(&dev->kobj, KOBJ_CHANGE, envp);
> -
>   	return 0;
> -
> -add_dev_err:
> -	mutex_unlock(&parent_list_lock);
> -	if (parent)
> -		mdev_put_parent(parent);
> -	else
> -		put_device(dev);
> -	return ret;
>   }
> -EXPORT_SYMBOL(mdev_register_device);
> +EXPORT_SYMBOL(mdev_register_parent);
>   
>   /*
> - * mdev_unregister_device : Unregister a parent device
> - * @dev: device structure representing parent device.
> - *
> - * Remove device from list of registered parent devices. Give a chance to free
> - * existing mediated devices for given device.
> + * mdev_unregister_parent : Unregister a parent device
> + * @parent: parent structure to unregister
>    */
> -
> -void mdev_unregister_device(struct device *dev)
> +void mdev_unregister_parent(struct mdev_parent *parent)
>   {
> -	struct mdev_parent *parent;
>   	char *env_string = "MDEV_STATE=unregistered";
>   	char *envp[] = { env_string, NULL };
>   
> -	mutex_lock(&parent_list_lock);
> -	parent = __find_parent_device(dev);
> -
> -	if (!parent) {
> -		mutex_unlock(&parent_list_lock);
> -		return;
> -	}
> -	dev_info(dev, "MDEV: Unregistering\n");
> -
> -	list_del(&parent->next);
> -	mutex_unlock(&parent_list_lock);
> +	dev_info(parent->dev, "MDEV: Unregistering\n");
>   
>   	down_write(&parent->unreg_sem);
> -
> -	class_compat_remove_link(mdev_bus_compat_class, dev, NULL);
> -
> -	device_for_each_child(dev, NULL, mdev_device_remove_cb);
> -
> +	class_compat_remove_link(mdev_bus_compat_class, parent->dev, NULL);
> +	device_for_each_child(parent->dev, NULL, mdev_device_remove_cb);
>   	parent_remove_sysfs_files(parent);
>   	up_write(&parent->unreg_sem);
>   
> -	mdev_put_parent(parent);
> -
> -	/* We still have the caller's reference to use for the uevent */
> -	kobject_uevent_env(&dev->kobj, KOBJ_CHANGE, envp);
> +	kobject_uevent_env(&parent->dev->kobj, KOBJ_CHANGE, envp);
>   }
> -EXPORT_SYMBOL(mdev_unregister_device);
> +EXPORT_SYMBOL(mdev_unregister_parent);
>   
>   static void mdev_device_release(struct device *dev)
>   {
> diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h
> index 7c9fc79f3d838..297f911fdc890 100644
> --- a/drivers/vfio/mdev/mdev_private.h
> +++ b/drivers/vfio/mdev/mdev_private.h
> @@ -13,17 +13,6 @@
>   int  mdev_bus_register(void);
>   void mdev_bus_unregister(void);
>   
> -struct mdev_parent {
> -	struct device *dev;
> -	struct mdev_driver *mdev_driver;
> -	struct kref ref;
> -	struct list_head next;
> -	struct kset *mdev_types_kset;
> -	struct list_head type_list;
> -	/* Synchronize device creation/removal with parent unregistration */
> -	struct rw_semaphore unreg_sem;
> -};
> -
>   struct mdev_type {
>   	struct kobject kobj;
>   	struct kobject *devices_kobj;
> @@ -48,16 +37,4 @@ void mdev_remove_sysfs_files(struct mdev_device *mdev);
>   int mdev_device_create(struct mdev_type *kobj, const guid_t *uuid);
>   int  mdev_device_remove(struct mdev_device *dev);
>   
> -void mdev_release_parent(struct kref *kref);
> -
> -static inline void mdev_get_parent(struct mdev_parent *parent)
> -{
> -	kref_get(&parent->ref);
> -}
> -
> -static inline void mdev_put_parent(struct mdev_parent *parent)
> -{
> -	kref_put(&parent->ref, mdev_release_parent);
> -}
> -
>   #endif /* MDEV_PRIVATE_H */
> diff --git a/drivers/vfio/mdev/mdev_sysfs.c b/drivers/vfio/mdev/mdev_sysfs.c
> index 0ccfeb3dda245..becce814aabfb 100644
> --- a/drivers/vfio/mdev/mdev_sysfs.c
> +++ b/drivers/vfio/mdev/mdev_sysfs.c
> @@ -83,7 +83,7 @@ static void mdev_type_release(struct kobject *kobj)
>   
>   	pr_debug("Releasing group %s\n", kobj->name);
>   	/* Pairs with the get in add_mdev_supported_type() */
> -	mdev_put_parent(type->parent);
> +	put_device(type->parent->dev);
>   	kfree(type);
>   }
>   
> @@ -112,7 +112,7 @@ static struct mdev_type *add_mdev_supported_type(struct mdev_parent *parent,
>   	type->kobj.kset = parent->mdev_types_kset;
>   	type->parent = parent;
>   	/* Pairs with the put in mdev_type_release() */
> -	mdev_get_parent(parent);
> +	get_device(parent->dev);
>   	type->type_group_id = type_group_id;
>   
>   	ret = kobject_init_and_add(&type->kobj, &mdev_type_ktype, NULL,
> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> index 555c1d015b5f0..327ce3e5c6b5f 100644
> --- a/include/linux/mdev.h
> +++ b/include/linux/mdev.h
> @@ -23,6 +23,16 @@ struct mdev_device {
>   	bool active;
>   };
>   
> +/* embedded into the struct device that the mdev devices hang off */
> +struct mdev_parent {
> +	struct device *dev;
> +	struct mdev_driver *mdev_driver;
> +	struct kset *mdev_types_kset;
> +	struct list_head type_list;
> +	/* Synchronize device creation/removal with parent unregistration */
> +	struct rw_semaphore unreg_sem;
> +};
> +
>   static inline struct mdev_device *to_mdev_device(struct device *dev)
>   {
>   	return container_of(dev, struct mdev_device, dev);
> @@ -75,8 +85,9 @@ static inline const guid_t *mdev_uuid(struct mdev_device *mdev)
>   
>   extern struct bus_type mdev_bus_type;
>   
> -int mdev_register_device(struct device *dev, struct mdev_driver *mdev_driver);
> -void mdev_unregister_device(struct device *dev);
> +int mdev_register_parent(struct mdev_parent *parent, struct device *dev,
> +		struct mdev_driver *mdev_driver);
> +void mdev_unregister_parent(struct mdev_parent *parent);
>   
>   int mdev_register_driver(struct mdev_driver *drv);
>   void mdev_unregister_driver(struct mdev_driver *drv);
> diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
> index 344c2901a82bf..f0967a81eabe7 100644
> --- a/samples/vfio-mdev/mbochs.c
> +++ b/samples/vfio-mdev/mbochs.c
> @@ -129,6 +129,7 @@ static dev_t		mbochs_devt;
>   static struct class	*mbochs_class;
>   static struct cdev	mbochs_cdev;
>   static struct device	mbochs_dev;
> +static struct mdev_parent mbochs_parent;
>   static atomic_t mbochs_avail_mbytes;
>   static const struct vfio_device_ops mbochs_dev_ops;
>   
> @@ -1457,7 +1458,7 @@ static int __init mbochs_dev_init(void)
>   	if (ret)
>   		goto err_class;
>   
> -	ret = mdev_register_device(&mbochs_dev, &mbochs_driver);
> +	ret = mdev_register_parent(&mbochs_parent, &mbochs_dev, &mbochs_driver);
>   	if (ret)
>   		goto err_device;
>   
> @@ -1478,7 +1479,7 @@ static int __init mbochs_dev_init(void)
>   static void __exit mbochs_dev_exit(void)
>   {
>   	mbochs_dev.bus = NULL;
> -	mdev_unregister_device(&mbochs_dev);
> +	mdev_unregister_parent(&mbochs_parent);
>   
>   	device_unregister(&mbochs_dev);
>   	mdev_unregister_driver(&mbochs_driver);
> diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c
> index e8c46eb2e2468..8ab88a1d149cb 100644
> --- a/samples/vfio-mdev/mdpy.c
> +++ b/samples/vfio-mdev/mdpy.c
> @@ -84,6 +84,7 @@ static dev_t		mdpy_devt;
>   static struct class	*mdpy_class;
>   static struct cdev	mdpy_cdev;
>   static struct device	mdpy_dev;
> +static struct mdev_parent mdpy_parent;
>   static u32		mdpy_count;
>   static const struct vfio_device_ops mdpy_dev_ops;
>   
> @@ -766,7 +767,7 @@ static int __init mdpy_dev_init(void)
>   	if (ret)
>   		goto err_class;
>   
> -	ret = mdev_register_device(&mdpy_dev, &mdpy_driver);
> +	ret = mdev_register_parent(&mdpy_parent, &mdpy_dev, &mdpy_driver);
>   	if (ret)
>   		goto err_device;
>   
> @@ -787,7 +788,7 @@ static int __init mdpy_dev_init(void)
>   static void __exit mdpy_dev_exit(void)
>   {
>   	mdpy_dev.bus = NULL;
> -	mdev_unregister_device(&mdpy_dev);
> +	mdev_unregister_parent(&mdpy_parent);
>   
>   	device_unregister(&mdpy_dev);
>   	mdev_unregister_driver(&mdpy_driver);
> diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
> index f42a59ed2e3fe..20136def93fdb 100644
> --- a/samples/vfio-mdev/mtty.c
> +++ b/samples/vfio-mdev/mtty.c
> @@ -74,6 +74,7 @@ static struct mtty_dev {
>   	struct cdev	vd_cdev;
>   	struct idr	vd_idr;
>   	struct device	dev;
> +	struct mdev_parent parent;
>   } mtty_dev;
>   
>   struct mdev_region_info {
> @@ -1352,7 +1353,8 @@ static int __init mtty_dev_init(void)
>   	if (ret)
>   		goto err_class;
>   
> -	ret = mdev_register_device(&mtty_dev.dev, &mtty_driver);
> +	ret = mdev_register_parent(&mtty_dev.parent, &mtty_dev.dev,
> +				   &mtty_driver);
>   	if (ret)
>   		goto err_device;
>   	return 0;
> @@ -1372,7 +1374,7 @@ static int __init mtty_dev_init(void)
>   static void __exit mtty_dev_exit(void)
>   {
>   	mtty_dev.dev.bus = NULL;
> -	mdev_unregister_device(&mtty_dev.dev);
> +	mdev_unregister_parent(&mtty_dev.parent);
>   
>   	device_unregister(&mtty_dev.dev);
>   	idr_destroy(&mtty_dev.vd_idr);