Re: [PATCH V8 3/6] mdev: introduce device specific ops

Cornelia Huck
2019-11-05T18:29:27Z

On Tue, 5 Nov 2019 10:44:18 -0700
Alex Williamson <alex.williamson@redhat.com> wrote:

> On Tue, 5 Nov 2019 17:50:25 +0100
> Cornelia Huck <cohuck@redhat.com> wrote:
>
> > On Tue, 5 Nov 2019 17:32:37 +0800
> > Jason Wang <jasowang@redhat.com> wrote:
> >
> > > Currently, except for the create and remove, the rest of
> > > mdev_parent_ops is designed for vfio-mdev driver only and may not help
> > > for kernel mdev driver. With the help of class id, this patch
> > > introduces device specific callbacks inside mdev_device
> > > structure. This allows different set of callback to be used by
> > > vfio-mdev and virtio-mdev.
> > >
> > > Reviewed-by: Parav Pandit <parav@mellanox.com>
> > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > ---
> > > .../driver-api/vfio-mediated-device.rst | 35 +++++++++----
> > > MAINTAINERS | 1 +
> > > drivers/gpu/drm/i915/gvt/kvmgt.c | 18 ++++---
> > > drivers/s390/cio/vfio_ccw_ops.c | 18 ++++---
> > > drivers/s390/crypto/vfio_ap_ops.c | 14 +++--
> > > drivers/vfio/mdev/mdev_core.c | 24 ++++++++-
> > > drivers/vfio/mdev/mdev_private.h | 5 ++
> > > drivers/vfio/mdev/vfio_mdev.c | 37 ++++++-------
> > > include/linux/mdev.h | 43 ++++-----------
> > > include/linux/mdev_vfio_ops.h | 52 +++++++++++++++++++
> > > samples/vfio-mdev/mbochs.c | 20 ++++---
> > > samples/vfio-mdev/mdpy.c | 20 ++++---
> > > samples/vfio-mdev/mtty.c | 18 ++++---
> > > 13 files changed, 206 insertions(+), 99 deletions(-)
> > > create mode 100644 include/linux/mdev_vfio_ops.h
> > >
> >
> > (...)
> >
> > > @@ -172,10 +163,34 @@ that a driver should use to unregister itself with the mdev core driver::
> > >
> > > extern void mdev_unregister_device(struct device *dev);
> > >
> > > -It is also required to specify the class_id in create() callback through::
> > > +As multiple types of mediated devices may be supported, class id needs
> > > +to be specified in the create callback(). This could be done
> >
> > The brackets should probably go behind 'create'?
> >
> > > +explicitly for the device that does not use on mdev bus for its
> >
> > "for devices that do not use the mdev bus" ?
> >
> > But why wouldn't they? I feel like I've missed some discussion here :/
>
> The device ops provide a route through mdev-core for known callbacks,
> which is primarily useful when we have 1:N relation between mdev bus
> driver and vendor drivers. The obvious example here is vfio-mdev,
> where we have GVT-g, vfio-ap, vfio-ccw, NVIDIA GRID, and various sample
> drivers all advertising vfio-mdev support via their class id. However,
> if we have a tightly coupled vendor driver and mdev bus driver, as the
> mlx5 support that Parav is developing, the claim is that they prefer
> not to expose any device ops and intend to interact directly with the
> mdev device. At least that's my understanding. Thanks,
>
> Alex

Ah, ok.

So maybe use the phrasing "devices that interact with the mdev device
directly" vs "devices that use device-specific ops" instead?

Not a strong critique, though.

>
> > > +operation through:
> > >
> > > int mdev_set_class(struct mdev_device *mdev, u16 id);
> > >
> > > +For the device that uses on the mdev bus for its operation, the
> > > class
> >
> > "For devices that use the mdev bus..."
> >
> > But same comment as above.
> >
> > > +should provide helper function to set class id and device
> > > specific +ops. E.g for vfio-mdev devices, the function to be
> > > called is:: +
> > > + int mdev_set_vfio_ops(struct mdev_device *mdev,
> > > + const struct mdev_vfio_device_ops
> > > *vfio_ops); +
> > > +The class id (set by this function to MDEV_CLASS_ID_VFIO) is
> > > used to +match a device with an mdev driver via its id table. The
> > > device +specific callbacks (specified in *vfio_ops) are
> > > obtainable via +mdev_get_vfio_ops() (for use by the mdev bus
> > > driver). A vfio-mdev +device (class id MDEV_CLASS_ID_VFIO) uses
> > > the following +device-specific ops:
> > > +
> > > +* open: open callback of vfio mediated device
> > > +* close: close callback of vfio mediated device
> > > +* ioctl: ioctl callback of vfio mediated device
> > > +* read : read emulation callback
> > > +* write: write emulation callback
> > > +* mmap: mmap emulation callback
> > > +
> > > Mediated Device Management Interface Through sysfs
> > > ==================================================
> >
> > Otherwise, looks good.
>