Re: [Qemu-devel] [PATCH v2 0/2] intel_iommu: Add support for translation for devices behind bridges

[Knut Omang]

On Sun, 2015-09-13 at 09:12 +1000, Benjamin Herrenschmidt wrote:
> On Sat, 2015-09-12 at 20:37 +0200, Knut Omang wrote:
> > As the thread went silent after our conclusions, I have made a
> > second
> > implementation for the Intel IOMMU according to this alternate
> > scheme,
> > It keeps the current API and handles the bus number resolution
> > lazily
> > within the IOMMU implementation, I will post the (single) patch as
> > v3
> > of this. 
> > 
> > Hopefully this is acceptable and can be leveraged to do a similar
> > rework, or be abstracted as generic functionality (?) for the other
> > architectures,..
> 
> Ah sorry, I meant to look at your email in more details and respond
> but
> it fell through the cracks.

I know how it is.. :-)

> I'm happy to have a look at your work and see how it applies to me,
> you
> can see my powernv code which also supports translation for devices
> behind bridges here (but doesn't do as much caching as q35 does):
> 
> https://github.com/ozbenh/qemu/commit/4e0ed1002f98fd97aa7ca3a48c74933
> d0343dd42

Looks conceptually similar - the caching part is probably not that
important, it just came natural as it evolved from the original
implementation. We are probably so far talking about max a few buses
and a few devices per bus, I suppose.

I suppose the best then now would be to stick to your suggestion of
getting the functionality in and let it mature, then look for any
optimization whether structural or performance wise,

> Which depends on:
> 
> https://github.com/ozbenh/qemu/commit/facedeba8811985ca20ac3dbad5d07e
> 1a10ea9b2
> 
> (Which I think Michael merged recently, I haven't checked).

Yes, I noticed while rebasing.

> Cheers,
> Ben.

Cheers,
Knut