On Thu, Feb 13, 2020 at 10:56:00AM -0500, Michael S. Tsirkin wrote: > On Thu, Feb 13, 2020 at 11:51:54AM -0400, Jason Gunthorpe wrote: > > > That bus is exactly what Greg KH proposed. There are other ways > > > to solve this I guess but this bikeshedding is getting tiring. > > > > This discussion was for a different goal, IMHO. > > Hmm couldn't find it anymore. What was the goal there in your opinion? I think it was largely talking about how to model things like ADI/SF/etc, plus stuff got very confused when the discussion tried to explain what mdev's role was vs the driver core. The standard driver model is a 'bus' driver provides the HW access (think PCI level things), and a 'hw driver' attaches to the bus device, and instantiates a 'subsystem device' (think netdev, rdma, etc) using some per-subsystem XXX_register(). The 'hw driver' pulls in functions from the 'subsystem' using a combination of callbacks and library-style calls so there is no code duplication. As a subsystem, vhost&vdpa should expect its 'HW driver' to bind to devices on busses, for instance I would expect: - A future SF/ADI/'virtual bus' as a child of multi-functional PCI device Exactly how this works is still under active discussion and is one place where Greg said 'use a bus'. - An existing PCI, platform, or other bus and device. No need for an extra bus here, PCI is the bus. - No bus, ie for a simulator or binding to a netdev. (existing vhost?) They point is that the HW driver's job is to adapt from the bus level interfaces (eg readl/writel) to the subsystem level (eg something like the vdpa_ops). For instance that Intel driver should be a pci_driver to bind to a struct pci_device for its VF and then call some 'vhost&vdpa' _register() function to pass its ops to the subsystem which in turn creates the struct device of the subsystem calls, common char devices, sysfs, etc and calls the driver's ops in response to uAPI calls. This is already almost how things were setup in v2 of the patches, near as I can see, just that a bus was inserted somehow instead of having only the vhost class. So it iwas confusing and the lifetime model becomes too complicated to implement correctly... Jason
