> -----Original Message-----
> From: Jason Gunthorpe <[email protected]>
> Sent: 28 October 2025 14:04
> To: Eric Auger <[email protected]>
> Cc: Nicolin Chen <[email protected]>; Shameer Kolothum
> <[email protected]>; [email protected]; qemu-
> [email protected]; [email protected]; [email protected];
> [email protected]; Nathan Chen <[email protected]>; Matt Ochs
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]
> Subject: Re: [PATCH v4 22/27] hw/arm/smmuv3-accel: Add support for ATS
>
> On Tue, Oct 28, 2025 at 02:51:29PM +0100, Eric Auger wrote:
> >
> >
> > On 10/28/25 2:41 PM, Jason Gunthorpe wrote:
> > > On Tue, Oct 28, 2025 at 02:21:32PM +0100, Eric Auger wrote:
> > >>
> > >> On 10/28/25 1:16 PM, Jason Gunthorpe wrote:
> > >>> On Mon, Oct 27, 2025 at 10:53:10AM -0700, Nicolin Chen wrote:
> > >>>
> > >>>> Hmm, that sounds a legit reason, though adding the ATS support to
> > >>>> the emulated SMMUv3 isn't seemingly a small effort...
> > >>> What is "emulated ATS" anyhow?
> > >> I guess it means implementing ATS translation requests and capability to
> > >> send ATS invalidations. something like:
> > >>
> > >>
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.
> kernel.org%2Fall%2F20250628180226.133285-1-clement.mathieu--
> drif%40eviden.com%2F&data=05%7C02%7Cskolothumtho%40nvidia.com%
> 7C9f9c8fc639214f54ca0808de162accab%7C43083d15727340c1b7db39efd
> 9ccc17a%7C0%7C0%7C638972570246014005%7CUnknown%7CTWFpbGZs
> b3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIs
> IkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=YQfzKiIcBbKj
> kIauHU8ELDk15jclFnFcevMMRf7LHF0%3D&reserved=0
> > > Why would you even want this? The cover letter didn't explain what the
> > > point was.
> >
> > well I am just concerned about exposing ATS support to emulated EPs
> > while we actually do not support it.
>
> Sure, that shouldn't be done. There is ACPI/DT tables indicating if the
> each device supports ATS and qemu should not be marking the emulated
> EPs as ATS capable in the first place..
>
> However, there is no big work with showing EPs as ATS capable. They
> don't implement an ATC and there is no concept of "translated address"
> inside qemu so the only requirement to make it "work" is to just NOP
> the ATC invalidation SMMU commands for those EPs.
The only case where an emulated endpoint can appear with SMMUv3
accel enabled is during a hot-plug scenario.
As mentioned elsewhere in this discussion, that can be handled by propagating
an error from the pci_device_iommu_address_space() path.
I will take a look at that if this is the main concern regarding ATS.
Thanks,
Shameer
