Re: [PATCH V13 6/6] docs: sample driver to demonstrate how to implement virtio-mdev framework

From: Jason Gunthorpe <jgg@mellanox.com>
To: Jason Wang <jasowang@redhat.com>
Cc: "rdunlap@infradead.org" <rdunlap@infradead.org>,
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	haotian.wang@sifiv
Subject: Re: [PATCH V13 6/6] docs: sample driver to demonstrate how to implement virtio-mdev framework
Date: Tue, 19 Nov 2019 16:39:30 +0000	[thread overview]
Message-ID: <20191119163927.GA4967@mellanox.com> (raw)
In-Reply-To: <9e786429-866d-e2ca-45f9-30c8e1ebece9@redhat.com>

On Tue, Nov 19, 2019 at 10:07:18PM +0800, Jason Wang wrote:
> 
> On 2019/11/19 下午8:40, Jason Gunthorpe wrote:
> > On Tue, Nov 19, 2019 at 11:03:39AM +0800, Jason Wang wrote:
> > > > Also, see the other conversations we are having about a "virtual" bus
> > > > and devices.  I do not want to have two different ways of doing the same
> > > > thing in the kernel at the same time please.  Please work together with
> > > > the Intel developers to solve this in a unified way, as you both
> > > > need/want the same thing here.
> > > Sure, some functions looks similar, but the "virtual" bus does not contain a
> > > management interface and it's not clear that how it can be used by userspace
> > > driver. For this series, sysfs/GUID based management interface is reused and
> > > we had a concrete example of how it would be used by userspace driver[1] and
> > > a real hardware driver implementation[2].
> > The lifecycle stuff should be re-used through a library of this guid
> > stuff, not by 'subclassing' mdev_device
> 
> But mdev provides more than lifecycle management: type management, IOMMU
> support etc. And more could be added in the future.

iommu support comes from dma_ops, not mdev.

mdev only provides vfio, and in this example there is no use of those
vfio ops - so it is not mdev.

> Having a library that serves exactly for the case of mdev seems less
> convenient than making mdev_device a 'parent class'.

It is the design pattern the device core uses

Jason
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