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

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Date:   Mon, 20 Jan 2020 16:56:06 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Gunthorpe <jgg@...lanox.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
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        Shahaf Shuler <shahafs@...lanox.com>,
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Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus

On Mon, Jan 20, 2020 at 05:50:55PM +0000, Jason Gunthorpe wrote:
> On Mon, Jan 20, 2020 at 07:17:26AM -0500, Michael S. Tsirkin wrote:
> > On Fri, Jan 17, 2020 at 01:54:42PM +0000, Jason Gunthorpe wrote:
> > > > 1) "virtio" vs "vhost", I implemented matching method for this in mdev
> > > > series, but it looks unnecessary for vDPA device driver to know about this.
> > > > Anyway we can use sysfs driver bind/unbind to switch drivers
> > > > 2) virtio device id and vendor id. I'm not sure we need this consider the
> > > > two drivers so far (virtio/vhost) are all bus drivers.
> > > 
> > > As we seem to be contemplating some dynamic creation of vdpa devices I
> > > think upon creation time it should be specified what mode they should
> > > run it and then all driver binding and autoloading should happen
> > > automatically. Telling the user to bind/unbind is a very poor
> > > experience.
> > 
> > Maybe but OTOH it's an existing interface. I think we can reasonably
> > start with bind/unbind and then add ability to specify
> > the mode later. bind/unbind come from core so they will be
> > maintained anyway.
> 
> Existing where?

Driver core.

> For vfio? vfio is the only thing I am aware doing
> that, and this is not vfio..
> 
> Jason


vfio is not doing anything. anyone can use a combination
of unbind and driver_override to attach a driver to a device.

It's not a great interface but it's there without any code,
and it will stay there without maintainance overhead
if we later add a nicer one.

-- 
MST