Re: [RFC PATCH 10/16] hw/arm/tegra241-cmdqv: Allocate vEVENTQ object

[Nicolin Chen <nicolinc@nvidia.com>]

On Tue, Dec 30, 2025 at 01:47:08AM -0800, Shameer Kolothum wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: 29 December 2025 19:50
> > To: Shameer Kolothum <skolothumtho@nvidia.com>
> > Cc: qemu-arm@nongnu.org; qemu-devel@nongnu.org;
> > eric.auger@redhat.com; peter.maydell@linaro.org; Nathan Chen
> > <nathanc@nvidia.com>; Matt Ochs <mochs@nvidia.com>; Jason Gunthorpe
> > <jgg@nvidia.com>; jonathan.cameron@huawei.com;
> > zhangfei.gao@linaro.org; zhenzhong.duan@intel.com; Krishnakant Jaju
> > <kjaju@nvidia.com>
> > Subject: Re: [RFC PATCH 10/16] hw/arm/tegra241-cmdqv: Allocate vEVENTQ
> > object
> > 
> > On Wed, Dec 10, 2025 at 01:37:31PM +0000, Shameer Kolothum wrote:
> > > @@ -259,11 +305,16 @@ static bool
> > tegra241_cmdqv_setup_vcmdq(Tegra241CMDQV *cmdqv, int index,
> > >          g_free(vcmdq);
> > >      }
> > >
> > > +    if (!tegra241_cmdqv_alloc_veventq(cmdqv, errp)) {
> > > +        return false;
> > > +    }
> > > +
> > 
> > I think this should be called in tegra241_cmdqv_alloc_viommu().
> 
> Should/Can we? _alloc_viommu() will happen before the Guest boot.

I think we can. vEVENTQ only needs vIOMMU ID. It's per VINTF v.s.
per VCMDQ (HW_QUEUE). So, it should follow vIOMMU.

Basically, we can allocate vIOMMU (VINTF) and its vEVENTQ even if
the VINTF doesn't contain any LVCMDQs, which are allocated/mapped
to the VINTF later via HW_QUEUE allocations.

> Unlike the SMMUv3 vEVENTQ for accel case, we restrict the hotplug
> use case when the tegra214-cmdqv is set. And as soon as Guest setup vCMDQ
> the vEVENTQ is enabled here. Do you see any issues with this approach?

Once guest OS is booting, !tegra241_cmdqv_alloc_veventq will fail
tegra241_cmdqv_setup_vcmdq while it cannot break the guest OS any
more. Then, the whole thing wouldn't work although guest OS runs?

Nicolin