Messages in this thread |  | | Subject | Re: [PATCH V2 3/5] vDPA: introduce vDPA bus | From | Jason Wang <> | Date | Fri, 14 Feb 2020 11:23:27 +0800 |
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On 2020/2/13 下午11:05, 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.
I'm confused here, are you suggesting to use class to create char device in vhost-vdpa? That's fine but the comment should go for vhost-vdpa patch.
> All the vdpa devices have the same basic > chardev interface and discover any semantic variations 'in band'
That's not true, char interface is only used for vhost. Kernel virtio driver does not need char dev but a device on the virtio bus.
> >>> 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.
This is demonstrated in the virito-vdpa driver. So if you want to use kernel virito driver for vDPA device, a bus is most straight forward.
> > 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.
Are you saying, e.g it's the charge of IFCVF driver to create vhost char dev and other stuffs?
> >>> 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.
I don't think so. Vhost is not the only programming interface for vDPA. We don't want a device that can only work for userspace drivers and only have a single set of userspace APIs.
Thanks
> > Jason >
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