RE: [PATCH 1/2] iommu: Add device ATS not supported capability

[Shameer Kolothum Thodi]

> -----Original Message-----
> From: Jason Gunthorpe <jgg@xxxxxxxx>
> Sent: 13 March 2026 16:49
> To: Shameer Kolothum Thodi <skolothumtho@xxxxxxxxxx>
> Cc: iommu@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; joro@xxxxxxxxxx;
> will@xxxxxxxxxx; robin.murphy@xxxxxxx; baolu.lu@xxxxxxxxxxxxxxx;
> kevin.tian@xxxxxxxxx; Nicolin Chen <nicolinc@xxxxxxxxxx>; Nathan Chen
> <nathanc@xxxxxxxxxx>; Matt Ochs <mochs@xxxxxxxxxx>; Krishnakant Jaju
> <kjaju@xxxxxxxxxx>
> Subject: Re: [PATCH 1/2] iommu: Add device ATS not supported capability
> 
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> 
> On Tue, Mar 03, 2026 at 03:03:47PM +0000, Shameer Kolothum wrote:
> > @@ -271,6 +271,8 @@ enum iommu_cap {
> >        */
> >       IOMMU_CAP_DEFERRED_FLUSH,
> >       IOMMU_CAP_DIRTY_TRACKING,       /* IOMMU supports dirty tracking */
> > +     /* ATS is not supported and not used on this device */
> > +     IOMMU_CAP_PCI_ATS_NOT_SUPPORTED,
> 
> Actually, on second thought, the kdoc should have more details about what
> supported means.
> 
> Does this mean ATS is available and could be turned on ?
> 
> Or does it mean ATS is on *right now* ?
> 
> The drivers should be changing ATS dynamically depending on what domain is
> attached.
> 
> I think the implementation follows the first option?

Yes. If we change it to IOMMU_CAP_PCI_ATS_SUPPORTED, it means ATS is
available and could be turned on. Will update.

Thanks,
Shameer