On Thu, Feb 13, 2020 at 11:05:42AM -0400, Jason Gunthorpe wrote: > 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. That's just a ton of useless code duplication, and a good chance to have minor variations in implementations confusing userspace. Instead, each device implement the same interface, and then vhost sits on top. > > > 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 That bus is exactly what Greg KH proposed. There are other ways to solve this I guess but this bikeshedding is getting tiring. Come on it's an internal kernel interface, if we feel it was a wrong direction to take we can change our minds later. Main thing is getting UAPI right. -- MST
