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[34.124.234.44]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-36b90c032fasm2002365a91.15.2026.05.28.09.32.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2026 09:32:29 -0700 (PDT) Date: Thu, 28 May 2026 16:32:23 +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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260528152930.GA3195266@nvidia.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260528_093232_208416_7BDE6D35 X-CRM114-Status: GOOD ( 13.74 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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? Am I missing the fact that CXL hardware could be already active and using ATS after the device_probe succeeds? Thanks, Praan