On Wed, Mar 12, 2025 at 04:34:18PM +0000, Shameerali Kolothum Thodi wrote: > Hi Eric, > > > -----Original Message----- > > From: Eric Auger <eric.au...@redhat.com> > > Sent: Wednesday, March 12, 2025 4:08 PM > > To: Shameerali Kolothum Thodi > > <shameerali.kolothum.th...@huawei.com>; qemu-...@nongnu.org; > > qemu-devel@nongnu.org > > Cc: 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: [RFC PATCH v2 05/20] hw/arm/smmuv3-accel: Associate a pxb- > > pcie bus > > > > Hi Shameer, > > > > > > On 3/11/25 3:10 PM, 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. > > why do we require a pxb-pcie root bus? why can't pci.0 root bus be used > > for simpler use cases (ie. I just want to passthough a NIC in > > accelerated mode). Or may pci.0 is also called a pax-pcie root bus? > > The idea was since pcie.0 is the default RC with virt, leave that to cases > where > we want to attach any emulated devices and use pxb-pcie based RCs for > vfio-pci.
The majority of management applications will never do anything other than a flat PCI(e) topology by default. Some might enable pxb-pcie as an optional but plenty won't ever support it. If you want to maximise the potential usefulness of the ssmmuv3-accel, and it is technically viable, it would be worth permitting choice of attachment to the root bus as an alteranative to the pxb. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
