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Thu, 28 May 2026 11:20:37 -0700 Date: Thu, 28 May 2026 11:20:35 -0700 From: Nicolin Chen To: Pranjal Shrivastava CC: Jason Gunthorpe , , , , , , , , , , , , , , , , 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> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW1PEPF0001615C:EE_|DS0PR12MB8813:EE_ X-MS-Office365-Filtering-Correlation-Id: acdaf9aa-a51b-4918-5f7f-08debce5e163 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|36860700016|82310400026|376014|1800799024|18002099003|4143699003|11063799006|56012099006|22082099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.118.232;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc7edge1.nvidia.com;CAT:NONE;SFS:(13230040)(7416014)(36860700016)(82310400026)(376014)(1800799024)(18002099003)(4143699003)(11063799006)(56012099006)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: icrxFBdifWINmP7ws2swmy03QeU8GgpesuMQ/LRGuN1G2oi98GBcDz9Q2NfObQfz2ifc/oBc/tXd2geoWMQUznQPZ1xVrmhy0okA3Hiv2wy7SsgFPpD06SYvejsrD08KOmU1IP7Q6WQBD/aID/lFkd1vm8fEc9eZCfZC7f/YUOn6eQ8sMCfM4Wk2NNVH6V35MQAwPPv6df3AWnoIYKAz8Fzxw56ipMA8VI0zUGDPkVLWfCqBdzDvEO5nGHBKwyBwgtwlEoQzCb2mjgc2pZPWpD8j1eQf1AK0qkid+Eol/uk2nP+vfDQ+HNXtDVS3E/3a+U7PJboAoxnf3SxIS1atT6KT20gWEP4QS959PvhVOSbFXb4GA2wTBK+YoltVs+WJdlCowwZUpZgaB6ZaUzPGmy2XV93H18Sp3xTD9KG/MdqMxf1mTGcNRpQjsTf+cO3O X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 May 2026 18:21:04.7117 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: acdaf9aa-a51b-4918-5f7f-08debce5e163 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.232];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: MW1PEPF0001615C.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB8813 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260528_112116_925275_8B8E3508 X-CRM114-Status: GOOD ( 20.14 ) 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 06:14:57PM +0000, Pranjal Shrivastava wrote: > 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? It would work in attach_dev(). I just felt cleaner to have it in probe(), paired with arm_smmu_free_cd_tables() in the release(). Thanks Nicolin