Subject: Re: [PATCH v4 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices

From: Nicolin Chen <[email-masked]>
Date: Wed, 20 May 2026 10:29:19 -0700

On Wed, May 20, 2026 at 11:20:43AM -0300, Jason Gunthorpe wrote:
> On Tue, May 19, 2026 at 06:04:18PM -0700, Nicolin Chen wrote:
> 
> > > Yeah, that's fair, so let's rename it to 
> > > 
> > > pci_translated_required()
> > > 
> > > ie the device requires translated requests to function. This is what
> > > CXL.cache implies (IIRC I was told the spec specifically says this)
> > > 
> > > Requiring translated requests implies you have to enable ATS in the
> > > system.
> > 
> > Perhaps we could let IOMMU drivers check:
> >   pci_cxl_is_cache_capable() || pci_dev_specific_is_pre_cxl()
> > directly?
> 
> I'd rather have a single function.

OK. Can we use pci_ats_required()?

CXL spec explicitly used "ATS" when stating the requirement of
CXL.cache). And it'd fit into the existing pci_ats_ functions.

Nicolin