RE: [PATCH v4 00/12] Initial support for SMMUv3 nested translation

Tian, Kevin
2025-02-19T08:34:15Z

> From: Baolu Lu <baolu.lu@linux.intel.com>
> Sent: Wednesday, February 19, 2025 10:10 AM
>
> On 2/18/25 21:03, Jason Gunthorpe wrote:
> > On Sat, Feb 15, 2025 at 05:53:13PM +0800, Baolu Lu wrote:
> >> On 2/14/25 20:41, Jason Gunthorpe wrote:
> >>> On Fri, Feb 14, 2025 at 01:39:52PM +0800, Baolu Lu wrote:
> >>>
> >>>> When the IOMMU is working in scalable mode, PASID and PRI are
> supported.
> >>>> ATS will always be enabled, even if the identity domain is attached to
> >>>> the device, because the PASID might use PRI, which depends on ATS
> >>>> functionality. This might not be the best choice, but it is the
> >>>> simplest and functional.
> >>> The arm driver keeps track of things and enables ATS when PASIDs are
> >>> present
> >> I am not aware of any VT-d hardware implementation that supports
> >> scalable mode but not PASID. If there were one, it would be worthwhile
> >> to add an optimization to avoid enabling ATS during probe if PASID is
> >> not supported.
> > I mean domains attached to PASIDs that need PRI/ATS/etc
>
> Yeah, that's a better solution. The PCI PRI/ATS features are only
> enabled when a domain that requires them is attached to it. I will
> consider it in the Intel driver later.
>

I didn't get the connection here. ATS can run w/o PASID per PCIe
spec. Why do we want to add a dependency on PASID here?