Hi Don,
> -----Original Message-----
> From: Donald Dutile <ddut...@redhat.com>
> Sent: Tuesday, March 18, 2025 10:12 PM
> To: Shameerali Kolothum Thodi
> <shameerali.kolothum.th...@huawei.com>; qemu-...@nongnu.org;
> qemu-devel@nongnu.org
> Cc: eric.au...@redhat.com; peter.mayd...@linaro.org; j...@nvidia.com;
> nicol...@nvidia.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: [RFC PATCH v2 05/20] hw/arm/smmuv3-accel: Associate a pxb-
> pcie bus
>
> Shameer,
>
> Hi!
>
> On 3/11/25 10:10 AM, Shameer Kolothum wrote:
> > User must associate a pxb-pcie root bus to smmuv3-accel
> > and that is set as the primary-bus for the smmu dev.
> >
> > Signed-off-by: Shameer Kolothum
> <shameerali.kolothum.th...@huawei.com>
> > ---
> > hw/arm/smmuv3-accel.c | 19 +++++++++++++++++++
> > 1 file changed, 19 insertions(+)
> >
> > diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
> > index c327661636..1471b65374 100644
> > --- a/hw/arm/smmuv3-accel.c
> > +++ b/hw/arm/smmuv3-accel.c
> > @@ -9,6 +9,21 @@
> > #include "qemu/osdep.h"
> >
> > #include "hw/arm/smmuv3-accel.h"
> > +#include "hw/pci/pci_bridge.h"
> > +
> > +static int smmuv3_accel_pxb_pcie_bus(Object *obj, void *opaque)
> > +{
> > + DeviceState *d = opaque;
> > +
> > + if (object_dynamic_cast(obj, "pxb-pcie-bus")) {
> > + PCIBus *bus = PCI_HOST_BRIDGE(obj->parent)->bus;
> > + if (d->parent_bus && !strcmp(bus->qbus.name, d->parent_bus-
> >name)) {
> > + object_property_set_link(OBJECT(d), "primary-bus", OBJECT(bus),
> > + &error_abort);
> > + }
> > + }
> > + return 0;
> > +}
> >
> > static void smmu_accel_realize(DeviceState *d, Error **errp)
> > {
> > @@ -17,6 +32,9 @@ static void smmu_accel_realize(DeviceState *d, Error
> **errp)
> > SysBusDevice *dev = SYS_BUS_DEVICE(d);
> > Error *local_err = NULL;
> >
> > + object_child_foreach_recursive(object_get_root(),
> > + smmuv3_accel_pxb_pcie_bus, d);
> > +
> > object_property_set_bool(OBJECT(dev), "accel", true, &error_abort);
> > c->parent_realize(d, &local_err);
> > if (local_err) {
> > @@ -33,6 +51,7 @@ static void smmuv3_accel_class_init(ObjectClass
> *klass, void *data)
> > device_class_set_parent_realize(dc, smmu_accel_realize,
> > &c->parent_realize);
> > dc->hotpluggable = false;
> > + dc->bus_type = TYPE_PCIE_BUS;
> > }
> >
> > static const TypeInfo smmuv3_accel_type_info = {
>
> I am not seeing the need for a pxb-pcie bus(switch) introduced for each
> 'accel'.
> Isn't the IORT able to define different SMMUs for different RIDs? if so,
> itsn't that sufficient
> to associate (define) an SMMU<->RID association without introducing a
> pxb-pcie?
> and again, I'm not sure how that improves/enables the device<->SMMU
> associativity?
Thanks for taking a look at the series. As discussed elsewhere in this
thread(with
Eric), normally in physical world (or atleast in the most common cases) SMMUv3
is attached to PCIe Root Complex and if you take a look at the IORT spec, it
describes
association of ID mappings between a RC node and SMMUV3 node.
And if my understanding is correct, in Qemu, only pxb-pcie allows you to add
extra root complexes even though it is still plugged to parent(pcie.0). ie, for
all
devices downstream it acts as a root complex but still plugged into a parent
pcie.0.
This allows us to add/describe multiple "smmuv3-accel" each associated with a
RC.
Having said that, current code only allows pxb-pcie root complexes avoiding
the pcie.0. The idea behind this was, user can use pcie.0 with a non accel
SMMUv3
for any emulated devices avoiding the performance bottlenecks we are
discussing for emulated dev+smmuv3-accel cases. But based on the feedback from
Eric and Daniel I will relax that restriction and will allow association with
pcie.0.
Thanks,
Shameer
>>> to root complexes.
> Feel free to enlighten me where I may have mis-read/interpreted the IORT
> & SMMUv3 specs.
>
> Thanks,
> - Don
>
