RE: [PATCH v3 1/6] hw/arm/smmuv3: Check SMMUv3 has PCIe Root Complex association

[Shameerali Kolothum Thodi via]

> -----Original Message-----
> From: Igor Mammedov <imamm...@redhat.com>
> Sent: Thursday, June 5, 2025 1:20 PM
> To: Shameerali Kolothum Thodi <shameerali.kolothum.th...@huawei.com>
> Cc: Shameer Kolothum via <qemu-devel@nongnu.org>; qemu-
> a...@nongnu.org; eric.au...@redhat.com; peter.mayd...@linaro.org;
> j...@nvidia.com; nicol...@nvidia.com; ddut...@redhat.com;
> berra...@redhat.com; nath...@nvidia.com; mo...@nvidia.com;
> smost...@google.com; Linuxarm <linux...@huawei.com>; Wangzhou (B)
> <wangzh...@hisilicon.com>; jiangkunkun <jiangkun...@huawei.com>;
> Jonathan Cameron <jonathan.came...@huawei.com>;
> zhangfei....@linaro.org
> Subject: Re: [PATCH v3 1/6] hw/arm/smmuv3: Check SMMUv3 has PCIe Root
> Complex association

[..]

> > > in QEMU with PCI, usually we specify bus to attach to with 'bus'
> property,
> > > wouldn't it better to rename "primary-bus" to 'bus' to be consistent
> with
> > > the rest of PCI code (and before "primary-bus" shows up as a CLI option,
> > > so far (before this series) it looks like it's an internal property)?
> >
> > That was tried in v2 and since SMMUv3 is not a pci device by itself(it is a
> > sysbus device) reusing the default "bus" property to establish an
> association
> > with a PCI bus created problems,
> > https://lore.kernel.org/qemu-devel/877c2ut0zk....@pond.sub.org/
> 
> that was an approach was trying to workaround by patching dc->bus_type,
> which is obviously wrong.
> 
> I'm not talking about changing device type or something similar,
> but about renaming 'primary-bus' property name to 'bus'

I have tried that earlier and gets this,
-device arm-smmuv3,bus=pcie.0,id=smmuv3.0: Device 'arm-smmuv3' can't go on PCIE 
bus

IIRC, the above mentioned patched dc->bus_type = TYPE_PCIE_BUS was used 
to avoid that.

Or am I missing something here?

> so it would be consistent interface wise with PCI or other QEMU devices
> that are attached to a bus.
> 
> > > > +    if (!bus || !object_dynamic_cast(bus->parent,
> > > TYPE_PCI_HOST_BRIDGE)) {
> > > Also looking at smmu_base_realize, it has NULL pointer check already.
> > > Which also rises question, shouldn't smmu_base_realize check for
> > > TYPE_PCI_HOST_BRIDGE as well (aka can smmu be attached to anything
> > > else but a host bridge)?
> >
> > Not at the moment in Qemu. Though the SMMUv3 specification allows it
> to
> > be associated with non-pci devices as well.
> 
> then perhaps move, the check to smmu_base_realize() for now?
> 
> if smmu + non-pci ever materialize, it can be refactored at that time.

Ok.

Thanks,
Shameer