Re: [PATCH V2 3/5] vDPA: introduce vDPA bus

On 2020/2/13 下午9:41, Jason Gunthorpe wrote:

On Thu, Feb 13, 2020 at 11:34:10AM +0800, Jason Wang wrote:

quoted

quoted

   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.

"

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.

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.

Thanks

I don't see a reason for VDPA to be creating busses..

Jason