Re: [PATCH v5 02/21] hw/pci: Introduce pci_device_get_viommu_cap()

[Nicolin Chen <nicolinc@nvidia.com>]

On Mon, Sep 01, 2025 at 02:35:29AM +0000, Duan, Zhenzhong wrote:
> >> I just noticed this change will conflict with your suggestion of using
> >HW_NESTED terminology.
> >> Let me know if you agree with this change or not?
> >
> >It wouldn't necessarily conflict. VIOMMU_FLAG_WANT_NESTING_PARENT
> >is a request, interchangeable with VIOMMU_FLAG_SUPPORT_HW_NESTED,
> >i.e. a cap.
> >
> >At the end of the day, they are fundamentally the same thing that
> >is to tell the core to allocate a nesting parent HWPT. The former
> >one is just more straightforward, avoiding confusing terms such as
> >"stage-1" and "nested".
> >
> >IMHO, you wouldn't even need the comments in the other thread, as
> >the flag explains clearly what it wants and what the core is doing.
> >
> >Also, once you use the "want" one, the "HW_NESTED" terminology will
> >not exist in the code.
> 
> OK, will use the *_flags and _WANT_* style, do you have suggestions
> for the name of vfio_device_viommu_get_nested() since "HW_NESTED"
> terminology will not exist, what about vfio_device_get_viommu_flags_W_N_P()?

I don't see it very necessary to have a specific API per flag. So,
it could be just:

    uint64_t viommu_flags = vfio_device_get_viommu_flags(vbasedev);

    if (viommu_flags & VIOMMU_FLAG_WANT_NEST_PARENT) {
        flags |= IOMMU_HWPT_ALLOC_NEST_PARENT;
    }
?

Thanks
Nic