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

From: Cornelia Huck <cohuck@redhat.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: stefanha@redhat.com, christophe.de.dinechin@gmail.com,
	kvm@vger.kernel.org, mst@redhat.com, airlied@linux.ie,
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	rodrigo.vivi@intel.com, xiao.w.wang@intel.com,
	freude@linux.ibm.com, zhenyuw@linux.intel.com,
	parav@mellanox.com, zhihong.wang@intel.com,
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	oberpar@linux.ibm.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, maxime.co
Subject: Re: [PATCH V8 3/6] mdev: introduce device specific ops
Date: Tue, 5 Nov 2019 19:28:51 +0100	[thread overview]
Message-ID: <20191105192851.40548978.cohuck__23157.8132182889$1572978583$gmane$org@redhat.com> (raw)
In-Reply-To: <20191105104418.1735d800@x1.home>

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.  
> 