On Thu, Feb 13, 2020 at 10:58:44PM +0800, Jason Wang wrote: > > On 2020/2/13 下午9:41, Jason Gunthorpe wrote: > > On Thu, Feb 13, 2020 at 11:34:10AM +0800, Jason Wang wrote: > > > > > > You have dev, type or > > > > class to choose from. Type is rarely used and doesn't seem to be used > > > > by vdpa, so class seems the right choice > > > > > > > > Jason > > > Yes, but my understanding is class and bus are mutually exclusive. So we > > > can't add a class to a device which is already attached on a bus. > > While I suppose there are variations, typically 'class' devices are > > user facing things and 'bus' devices are internal facing (ie like a > > PCI device) > > > Though all vDPA devices have the same programming interface, but the > semantic is different. So it looks to me that use bus complies what > class.rst said: > > " > > Each device class defines a set of semantics and a programming interface > that devices of that class adhere to. Device drivers are the > implementation of that programming interface for a particular device on > a particular bus. > > " Here we are talking about the /dev/XX node that provides the programming interface. All the vdpa devices have the same basic chardev interface and discover any semantic variations 'in band' > > So why is this using a bus? VDPA is a user facing object, so the > > driver should create a class vhost_vdpa device directly, and that > > driver should live in the drivers/vhost/ directory. > > This is because we want vDPA to be generic for being used by different > drivers which is not limited to vhost-vdpa. E.g in this series, it allows > vDPA to be used by kernel virtio drivers. And in the future, we will > probably introduce more drivers in the future. I don't see how that connects with using a bus. Every class of virtio traffic is going to need a special HW driver to enable VDPA, that special driver can create the correct vhost side class device. > > For the PCI VF case this driver would bind to a PCI device like > > everything else > > > > For our future SF/ADI cases the driver would bind to some > > SF/ADI/whatever device on a bus. > > All these driver will still be bound to their own bus (PCI or other). And > what the driver needs is to present a vDPA device to virtual vDPA bus on > top. Again, I can't see any reason to inject a 'vdpa virtual bus' on top. That seems like mis-using the driver core. Jason
