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

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Message-ID: <20200213134128.GV4271@mellanox.com>
Date:   Thu, 13 Feb 2020 09:41:28 -0400
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
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Subject: Re: [PATCH V2 3/5] vDPA: introduce vDPA bus

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)

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.

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.

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

Jason