Re: [PATCH rc v2] iommu/arm-smmu-v3: Fix inconsistent ATS state tracking

[Nicolin Chen <nicolinc@nvidia.com>]

On Mon, May 04, 2026 at 08:40:33PM +0000, Pranjal Shrivastava wrote:
> On Mon, May 04, 2026 at 01:23:06PM -0700, Nicolin Chen wrote:
> > On Mon, May 04, 2026 at 07:33:07PM +0000, Pranjal Shrivastava wrote:
> > > On Mon, May 04, 2026 at 11:01:42AM -0700, Nicolin Chen wrote:
> > > > On Mon, May 04, 2026 at 04:38:42PM +0000, Pranjal Shrivastava wrote:
> > > and then in attach_prepare we can add the ats check for safety:
> > > 
> > >         if (!state->ats_enabled && master->ats_enabled) {
> > >                 pci_disable_ats(to_pci_dev(master->dev));
> > > 
> > > +               if (pdev->ats_enabled)
> > > +                       pci_disable_ats(to_pci_dev(master->dev));
> > 
> > master->ats_enabled is redundant if we check pdev->ats_enabled.
> > 
> 
> BTW, is it really redundant? I assume it represents the driver's state 
> machine? I believe the condition:
> 
> if (!state->ats_enabled && master->ats_enabled) 
> 
> translates to: The current state has ATS active, but the new target
> state is to have them inactive. Isn't that the case?

That's fair enough.

We would need an dev_is_pci(), so having master->ats_enabled makes
sense.

> > If we add a gate here, should add to pci_enable_ats() too?
> > 
> 
> I see that pci_enable_ats already checks for it:
> 
> 	if (WARN_ON(dev->ats_enabled))
> 		return -EBUSY;

I see, then we could probably leave that so future corner case can
warn us. IOW, yea, I think gating pci_disable_ats() only is fine.

Thanks
Nicolin