This is my alternative take on this series from Jason: https://lore.kernel.org/dri-devel/87czsszi9i.fsf@xxxxxxxxxx/T/ The mdev/vfio parts are exactly the same, but this solves the driver core changes for the direct probing without the in/out flag that Greg hated, which cause a little more work, but probably make the result better. Original decription from Jason below: The mdev bus's core part for managing the lifecycle of devices is mostly as one would expect for a driver core bus subsystem. However instead of having a normal 'struct device_driver' and binding the actual mdev drivers through the standard driver core mechanisms it open codes this with the struct mdev_parent_ops and provides a single driver that shims between the VFIO core's struct vfio_device and the actual device driver. Instead, allow mdev drivers implement an actual struct mdev_driver and directly call vfio_register_group_dev() in the probe() function for the mdev. Arrange to bind the created mdev_device to the mdev_driver that is provided by the end driver. The actual execution flow doesn't change much, eg what was parent_ops->create is now device_driver->probe and it is called at almost the exact same time - except under the normal control of the driver core. Ultimately converting all the drivers unlocks a fair number of additional VFIO simplifications and cleanups. Changes since v1: - avoid warning spam for successful probes - improve the probe_count protection
