On Mon, 18 Jan 2021 14:16:26 -0400 Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > On Mon, Jan 18, 2021 at 05:00:09PM +0100, Cornelia Huck wrote: > > > > You can say that all the HW specific things are in the mlx5_vfio_pci > > > driver. It is an unusual driver because it must bind to both the PCI > > > VF with a pci_driver and to the mlx5_core PF using an > > > auxiliary_driver. This is needed for the object lifetimes to be > > > correct. > > > > Hm... I might be confused about the usage of the term 'driver' here. > > IIUC, there are two drivers, one on the pci bus and one on the > > auxiliary bus. Is the 'driver' you're talking about here more the > > module you load (and not a driver in the driver core sense?) > > Here "driver" would be the common term meaning the code that realizes > a subsytem for HW - so mlx5_vfio_pci is a VFIO driver because it > ultimately creates a /dev/vfio* through the vfio subsystem. > > The same way we usually call something like mlx5_en an "ethernet > driver" not just a "pci driver" > > > Yes, sure. But it also shows that mlx5_vfio_pci aka the device-specific > > code is rather small in comparison to the common vfio-pci code. > > Therefore my question whether it will gain more specific changes (that > > cannot be covered via the auxiliary driver.) > > I'm not sure what you mean "via the auxiliary driver" - there is only > one mlx5_vfio_pci, and the non-RFC version with all the migration code > is fairly big. > > The pci_driver contributes a 'struct pci_device *' and the > auxiliary_driver contributes a 'struct mlx5_core_dev *'. mlx5_vfio_pci > fuses them together into a VFIO device. Depending on the VFIO > callback, it may use an API from the pci_device or from the > mlx5_core_dev device, or both. Let's rephrase my question a bit: This proposal splits the existing vfio-pci driver into a "core" component and code actually implementing the "driver" part. For mlx5, an alternative "driver" is introduced that reuses the "core" component and also hooks into mlx5-specific code parts via the auxiliary device framework. (IIUC, the plan is to make existing special cases for devices follow mlx5's lead later.) I've been thinking of an alternative split: Keep vfio-pci as it is now, but add an auxiliary device. For mlx5, an auxiliary device_driver can match to that device and implement mlx5-specific things. From the code in this RFC, it is not clear to me whether this would be feasible: most callbacks seem to simply forward to the core component, and that might be possible to be done by a purely auxiliary device_driver; but this may or may not work well for additional functionality. I guess my question is: into which callbacks will the additional functionality hook? If there's no good way to do what they need to do without manipulating the vfio-pci calls, my proposal will not work, and this proposal looks like the better way. But it's hard to tell without seeing the code, which is why I'm asking :)
