RE: [PATCH v2 1/6] hw/arm/smmuv3: Add support to associate a PCIe RC

[Shameerali Kolothum Thodi via <qemu-arm@nongnu.org>]

> -----Original Message-----
> From: Daniel P. Berrangé <berrange@redhat.com>
> Sent: Friday, May 9, 2025 9:14 AM
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
> Cc: Donald Dutile <ddutile@redhat.com>; Markus Armbruster
> <armbru@redhat.com>; Shameer Kolothum via <qemu-
> devel@nongnu.org>; qemu-arm@nongnu.org; eric.auger@redhat.com;
> peter.maydell@linaro.org; jgg@nvidia.com; nicolinc@nvidia.com;
> nathanc@nvidia.com; mochs@nvidia.com; smostafa@google.com; Linuxarm
> <linuxarm@huawei.com>; Wangzhou (B) <wangzhou1@hisilicon.com>;
> jiangkunkun <jiangkunkun@huawei.com>; Jonathan Cameron
> <jonathan.cameron@huawei.com>; zhangfei.gao@linaro.org
> Subject: Re: [PATCH v2 1/6] hw/arm/smmuv3: Add support to associate a
> PCIe RC
> 

[...]

> > > - bus pcie, id=pcie.<num>
> > > - device iommu=[intel_iommu|smmuv3|amd_iommu], bus=[sysbus |
> > > pcie.<num>], id=iommu.<num>
> > > [Yes, I'm sticking with 'iommu' as the generic naming... everyone thinks
> of
> > > device SMMUs as IOMMUs,
> > >   and QEMU should have a more arch-agnostic naming of these system
> > > functions. ]
> >
> > Ok. But to circle back to what originally started this discussion—how
> important
> > is it to rely on the default "bus" in this case? As Markus pointed out,
> SMMUv3
> > is a platform device on the sysbus, so its default bus type can’t point to
> something
> > like PCIe. QEMU doesn’t currently support that.
> >
> > The main motivation for using the default "bus" so far has been to have
> better
> > compatibility with libvirt. Would libvirt be flexible enough if we switched
> to using
> > something like a "primary-bus" property instead?
> 
> Sorry if my previous comments misled you, when I previously talked about
> linking via a "bus" property I was not considering the fact that "bus"
> is a special property inside QEMU. From a libvirt POV we don't care what
> the property is call - it was just intended to be a general illustration
> of cross-referencing the iommu with the PCI bus it needed to be associated
> with.

Cool. That makes life easier 😊

Thanks,
Shameer