Re: [Xen-devel] [PATCH v6 01/14] iommu: introduce the concept of BFN...

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Paul Durrant [mailto:Paul.Durrant@xxxxxxxxxx]
> Sent: Thursday, September 6, 2018 10:54 PM
> 
> > -----Original Message-----
> > From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> > Sent: 06 September 2018 14:13
> > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> > Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>; Julien Grall
> > <julien.grall@xxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>; Stefano
> > Stabellini <sstabellini@xxxxxxxxxx>; xen-devel <xen-
> > devel@xxxxxxxxxxxxxxxxxxxx>
> > Subject: RE: [Xen-devel] [PATCH v6 01/14] iommu: introduce the concept
> of
> > BFN...
> >
> > >>> On 06.09.18 at 12:36, <Paul.Durrant@xxxxxxxxxx> wrote:
> > >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> > >> Sent: 05 September 2018 10:39
> > >>
> > >> >>> On 05.09.18 at 11:13, <Paul.Durrant@xxxxxxxxxx> wrote:
> > >> > Personally I think 'bus address' is commonly enough used term for
> > >> addresses
> > >> > used by devices for DMA. Indeed we have already 'dev_bus_addr' in
> > the
> > >> grant
> > >> > map and unmap hypercalls. So baddr and bfn seem like ok terms to
> me.
> > It's
> > >> > also not impossible to rename these later if they prove problematic.
> > >>
> > >> But that's the point - the names are problematic (to me): I
> permanently
> > >> have to remind myself that they do _not_ refer to the addresses as
> > >> seen when accessing memory, but the ones going _into_ the IOMMU.
> > >
> > > Ok. Could we agree on 'IOFN' then? I think 'iova' and 'io address' are
> also
> > > reasonably widely used terms to refer to address from a device's PoV.
> I'd
> > > really like to unblock these early patches.
> >
> > Hmm, earlier I had indicated I'd prefer DFN (as this make clear whose
> > view we are talking about). Kevin seemed to prefer DFN too, just with
> > a different association for D (which, as said, I consider unhelpful). So
> > is there a particular reason you're now suggesting IOFN nevertheless?
> 
> It was the ambiguity and lack of agreement over the 'D' that made me think
> that the other alternative would be better.
> Kevin, would you be ok with 'IOFN'?
> 

My problem with DFN is when combining D with address then "device 
address" is not very clear to me while interpreting D as DMA is also
not that clear from Jan's point.

I didn't see a perfect candidate without causing any ambiguity - at this
point I feel IOFN/IOVA might not be the best one but it wins to me when
considering the fact that it is widely used term in other places (e.g. in vtd 
spec, in Linux vfio/iommu driver, etc.). 

Thanks
Kevin

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