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Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus
To:     Jason Gunthorpe <jgg@mellanox.com>
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 <20200117135435.GU20978@mellanox.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <ea4639ba-d991-c95c-8cb1-48588e5b42c0@redhat.com>
Date:   Mon, 20 Jan 2020 15:50:01 +0800
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On 2020/1/17 =E4=B8=8B=E5=8D=889:54, Jason Gunthorpe wrote:
> On Fri, Jan 17, 2020 at 11:03:12AM +0800, Jason Wang wrote:
>> On 2020/1/16 =E4=B8=8B=E5=8D=8811:22, Jason Gunthorpe wrote:
>>> On Thu, Jan 16, 2020 at 08:42:29PM +0800, Jason Wang wrote:
>>>> vDPA device is a device that uses a datapath which complies with the
>>>> virtio specifications with vendor specific control path. vDPA device=
s
>>>> can be both physically located on the hardware or emulated by
>>>> software. vDPA hardware devices are usually implemented through PCIE
>>>> with the following types:
>>>>
>>>> - PF (Physical Function) - A single Physical Function
>>>> - VF (Virtual Function) - Device that supports single root I/O
>>>>     virtualization (SR-IOV). Its Virtual Function (VF) represents a
>>>>     virtualized instance of the device that can be assigned to diffe=
rent
>>>>     partitions
>>>> - VDEV (Virtual Device) - With technologies such as Intel Scalable
>>>>     IOV, a virtual device composed by host OS utilizing one or more
>>>>     ADIs.
>>>> - SF (Sub function) - Vendor specific interface to slice the Physica=
l
>>>>     Function to multiple sub functions that can be assigned to diffe=
rent
>>>>     partitions as virtual devices.
>>> I really hope we don't end up with two different ways to spell this
>>> same thing.
>> I think you meant ADI vs SF. It looks to me that ADI is limited to the=
 scope
>> of scalable IOV but SF not.
> I think if one looks carefully you'd find that SF and ADI are using
> very similar techiniques. For instance we'd also like to use the code
> reorg of the MSIX vector setup with SFs that Intel is calling IMS.
>
> Really SIOV is simply a bundle of pre-existing stuff under a tidy
> name, whatever code skeleton we come up with for SFs should be re-used
> for ADI.


Ok, but do you prefer to mention ADI only for the next version?


>
>>> Shouldn't there be a device/driver matching process of some kind?
>>
>> The question is what do we want do match here.
>>
>> 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.
>
> Jason


Ok, I will add the type (virtio vs vhost) and driver matching method back=
.

Thanks