RE: Plan for /dev/ioasid RFC v2

[Tian, Kevin]

> From: Leon Romanovsky <leon@xxxxxxxxxx>
> Sent: Wednesday, June 9, 2021 5:02 PM
> 
> On Mon, Jun 07, 2021 at 02:58:18AM +0000, Tian, Kevin wrote:
> > Hi, all,
> 
> <...>
> 
> > (Remaining opens in v1)
> 
> <...>
> 
> > -   Device-centric (Jason) vs. group-centric (David) uAPI. David is not fully
> >     convinced yet. Based on discussion v2 will continue to have ioasid uAPI
> >     being device-centric (but it's fine for vfio to be group-centric). A new
> >     section will be added to elaborate this part;
> 
> <...>
> 
> > (Adopted suggestions)
> 
> <...>
> 
> > -   (Jason) Addition of device label allows per-device capability/format
> >     check before IOASIDs are created. This leads to another major uAPI
> >     change in v2 - specify format info when creating an IOASID (mapping
> >     protocol, nesting, coherent, etc.). User is expected to check per-device
> >     format and then set proper format for IOASID upon to-be-attached
> >     device;
> 
> Sorry for my naive question, I still didn't read all v1 thread and maybe
> the answer is already written, but will ask anyway.
> 
> Doesn't this adopted suggestion to allow device-specific configuration
> actually means that uAPI should be device-centric?
> 
> User already needs to be aware of device, configure it explicitly, maybe
> gracefully clean it later, it looks like not so much left to be group-centric.
> 

Yes, this is what v2 will lean toward. /dev/ioasid reports format info and 
handle IOASID attachment per device. VFIO could still keep its group-
centric uAPI, but in the end it needs bind each device in the group to 
IOASID FD one-by-one. 

Thanks
Kevin