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[34.124.234.44]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-36b908f8f80sm2156136a91.5.2026.05.28.11.15.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2026 11:15:04 -0700 (PDT) Date: Thu, 28 May 2026 18:14:57 +0000 From: Pranjal Shrivastava To: Jason Gunthorpe Cc: Nicolin Chen , will@kernel.org, robin.murphy@arm.com, joro@8bytes.org, bhelgaas@google.com, baolu.lu@linux.intel.com, kevin.tian@intel.com, miko.lenczewski@arm.com, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, dan.j.williams@intel.com, jonathan.cameron@huawei.com, vsethi@nvidia.com, linux-cxl@vger.kernel.org, nirmoyd@nvidia.com Subject: Re: [PATCH v6 3/3] iommu/arm-smmu-v3: Allow ATS to be always on Message-ID: References: <18bb6f421b3be891caa8f1fb50f3a4d56b52d5be.1779392420.git.nicolinc@nvidia.com> <20260528152930.GA3195266@nvidia.com> <20260528180018.GB3195266@nvidia.com> Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260528180018.GB3195266@nvidia.com> On Thu, May 28, 2026 at 03:00:18PM -0300, Jason Gunthorpe wrote: > On Thu, May 28, 2026 at 04:32:23PM +0000, Pranjal Shrivastava wrote: > > On Thu, May 28, 2026 at 12:29:30PM -0300, Jason Gunthorpe wrote: > > > On Thu, May 28, 2026 at 03:24:40PM +0000, Pranjal Shrivastava wrote: > > > > > > > > + master->ats_always_on = true; > > > > > + > > > > > + return arm_smmu_alloc_cd_tables(master); > > > > > > > > Nit: I'm not sure if I'm getting this right, are we saying we *need* to > > > > allocate CDs for CXL.cache cases in the probe itself because STE.EATS > > > > requires Config=Translate with S1DSS in bypass? > > > > > > Yeah, basically. > > > > > > Effectively the ARM rules for enabling ATS and Bypass together require > > > a valid CD table pointer. > > > > Ack. But do we expect transactions before attach_dev? What'd happen if > > we don't allocate CDs here? > > It can be done at any point before a non-abort STE is formed. > > The core code pretty much does this immediately after probe so there > isn't much point in moving it later. > Right.. that's what I'm not understanding clearly, if the STE is Abort anyway during probe, why are we breaking the alloc-at-attach convention? Usually, we allocate CD tables in the first attach_dev call. Why does that not work here? [Disclaimer: Not a pushback, just trying to understand the requirement] Praan