vfio: Mediated device Core driver

Design for Mediated Device Driver:
Main purpose of this driver is to provide a common interface for mediated
device management that can be used by different drivers of different
devices.

This module provides a generic interface to create the device, add it to
mediated bus, add device to IOMMU group and then add it to vfio group.

Below is the high Level block diagram, with Nvidia, Intel and IBM devices
as example, since these are the devices which are going to actively use
this module as of now.

 +---------------+
 |               |
 | +-----------+ |  mdev_register_driver() +--------------+
 | |           | +<------------------------+ __init()     |
 | |  mdev     | |                         |              |
 | |  bus      | +------------------------>+              |<-> VFIO user
 | |  driver   | |     probe()/remove()    | vfio_mdev.ko |    APIs
 | |           | |                         |              |
 | +-----------+ |                         +--------------+
 |               |
 |  MDEV CORE    |
 |   MODULE      |
 |   mdev.ko     |
 | +-----------+ |  mdev_register_device() +--------------+
 | |           | +<------------------------+              |
 | |           | |                         |  nvidia.ko   |<-> physical
 | |           | +------------------------>+              |    device
 | |           | |        callback         +--------------+
 | | Physical  | |
 | |  device   | |  mdev_register_device() +--------------+
 | | interface | |<------------------------+              |
 | |           | |                         |  i915.ko     |<-> physical
 | |           | +------------------------>+              |    device
 | |           | |        callback         +--------------+
 | |           | |
 | |           | |  mdev_register_device() +--------------+
 | |           | +<------------------------+              |
 | |           | |                         | ccw_device.ko|<-> physical
 | |           | +------------------------>+              |    device
 | |           | |        callback         +--------------+
 | +-----------+ |
 +---------------+

Core driver provides two types of registration interfaces:
1. Registration interface for mediated bus driver:

/**
  * struct mdev_driver - Mediated device's driver
  * @name: driver name
  * @probe: called when new device created
  * @remove:called when device removed
  * @driver:device driver structure
  *
  **/
struct mdev_driver {
         const char *name;
         int  (*probe)  (struct device *dev);
         void (*remove) (struct device *dev);
         struct device_driver    driver;
};

Mediated bus driver for mdev device should use this interface to register
and unregister with core driver respectively:

int  mdev_register_driver(struct mdev_driver *drv, struct module *owner);
void mdev_unregister_driver(struct mdev_driver *drv);

Mediated bus driver is responsible to add/delete mediated devices to/from
VFIO group when devices are bound and unbound to the driver.

2. Physical device driver interface
This interface provides vendor driver the set APIs to manage physical
device related work in its driver. APIs are :

* dev_attr_groups: attributes of the parent device.
* mdev_attr_groups: attributes of the mediated device.
* supported_type_groups: attributes to define supported type. This is
			 mandatory field.
* create: to allocate basic resources in vendor driver for a mediated
         device. This is mandatory to be provided by vendor driver.
* remove: to free resources in vendor driver when mediated device is
         destroyed. This is mandatory to be provided by vendor driver.
* open: open callback of mediated device
* release: release callback of mediated device
* read : read emulation callback.
* write: write emulation callback.
* ioctl: ioctl callback.
* mmap: mmap emulation callback.

Drivers should use these interfaces to register and unregister device to
mdev core driver respectively:

extern int  mdev_register_device(struct device *dev,
                                 const struct parent_ops *ops);
extern void mdev_unregister_device(struct device *dev);

There are no locks to serialize above callbacks in mdev driver and
vfio_mdev driver. If required, vendor driver can have locks to serialize
above APIs in their driver.

Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
Signed-off-by: Neo Jia <cjia@nvidia.com>
Reviewed-by: Jike Song <jike.song@intel.com>
Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>