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Thu, 28 May 2026 15:13:50 -0700 Date: Thu, 28 May 2026 15:13:48 -0700 From: Nicolin Chen To: Pranjal Shrivastava CC: , Will Deacon , Joerg Roedel , Robin Murphy , Jason Gunthorpe , Mostafa Saleh , Daniel Mentz , Ashish Mhetre , Subject: Re: [PATCH v7 08/11] iommu/arm-smmu-v3: Implement pm_runtime & system sleep ops Message-ID: References: <20260527221407.1756491-1-praan@google.com> <20260527221407.1756491-9-praan@google.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: SN1PEPF000397B0:EE_|SN7PR12MB8770:EE_ X-MS-Office365-Filtering-Correlation-Id: 2f3079a1-f67d-4818-271c-08debd067286 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|82310400026|376014|36860700016|18002099003|11063799006|4143699003|22082099003|56012099006; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230040)(1800799024)(82310400026)(376014)(36860700016)(18002099003)(11063799006)(4143699003)(22082099003)(56012099006);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 1t1tq+PPZBHNDQDE15HxlwdXAfbopBEKkEUWvlHlK9l8YCyZ2HG6Co2LOpXCFmhRe2HdPg4iTOMQWBJ/pflWOHwnjXXlMoaG+0bWaWbEzZEVPTVj4p3f0mi4V64WjzApQTUFzF2su/4R35g7OlbIFCfQAFvKPr4Gu3prn7+JtsexPSRBU/Tno0Jwqws8XNT+HzfBUy7/6LKTySSaIwGVSuFHPHYSvO0qWyhMfNAvHuxFfbALEdcGT3ACVaNWMVZZJWGtGO1xXFQIUr2fC8IchggTxNnABAVDHD+fHFkg5fpDDzpqiMkSSIdXDpGUyU6cvEnA0j3IJSGkeMgkhyKrB4zq4PBqVAkiyiELQnp/Ce3+LGks1gLF2+IN19KR6YjAjLj8LyjepU3N/b26rzW/8Bj90agSWJd9bsayZxKJpSavpeqpmfJf4tQqL8tqy9k8 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 May 2026 22:14:12.0483 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2f3079a1-f67d-4818-271c-08debd067286 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: SN1PEPF000397B0.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB8770 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260528_151420_984571_B6DADAB0 X-CRM114-Status: GOOD ( 20.56 ) 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 09:21:22PM +0000, Pranjal Shrivastava wrote: > On Thu, May 28, 2026 at 12:39:46PM -0700, Nicolin Chen wrote: > > On Wed, May 27, 2026 at 10:14:04PM +0000, Pranjal Shrivastava wrote: > > > @@ -789,7 +822,8 @@ int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu, > > > /* b. Stop gathering work by clearing the owned flag */ > > > prod = atomic_fetch_andnot_relaxed(CMDQ_PROD_OWNED_FLAG, > > > &cmdq->q.llq.atomic.prod); > > > - prod &= ~CMDQ_PROD_OWNED_FLAG; > > > + /* Strip all metadata flags */ > > > + prod &= CMDQ_PROD_IDX_MASK; > > > > Should its prior atomic_fetch_andnot_relaxed() call do something > > about the CMDQ_PROD_STOP_FLAG as well? > > Umm.. No, the atomic_fetch_andnot_relaxed() call must leave the STOP_FLAG. > This block is the owner-publish phase, which occurs *after* the Point of > Commitment. If a submission successfully reserved its indices before the > gate closed, it shall be allowed to finish. > > If the owner thread cleared the STOP_FLAG here in the global memory, it > would prematurely re-open the gate, allowing new racing submissions to > leak in during the suspend sequence. > > The algorithm works mainly because the RPM callbacks are the only ones > that are allowed to manipulate this flag. That reads plausible to me. It would be nicer to leave a brief note inline. > > Should it handle a secondary_cmdq? > > No, I don't think we need to check secondary queues here. The STOP_FLAG > being set on the primary CMDQ during the suspend should suffice to > indicate the entire SMMU's power state. That's why the function takes in > the smmu ptr and not the cmdq. But if we don't set STOP flag to the secondary_cmdq, wouldn't the drain() timeout on the secondary_cmdq that does not elide? Nicolin