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Thu, 28 May 2026 12:41:36 -0700 Date: Thu, 28 May 2026 12:41:35 -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 07/11] iommu/arm-smmu-v3: Add CMDQ_PROD_STOP_FLAG to gate CMDQ submissions Message-ID: References: <20260527221407.1756491-1-praan@google.com> <20260527221407.1756491-8-praan@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260527221407.1756491-8-praan@google.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PEPF00000140:EE_|CH3PR12MB8996:EE_ X-MS-Office365-Filtering-Correlation-Id: 1f68088d-3ae9-438a-e021-08debcf12a4e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|82310400026|36860700016|1800799024|3023799007|18002099003|22082099003|11063799006|56012099006|4143699003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 8jl+sLBi89h617LzMKtCITipT+x/fBgNSJA+Ttqrgm0xsFn9Fo2zsnwNQoA37LqdxuKDj12aIpuJVB8kvXD/eauuthtGVD0xhguLPNrc2UlJK6lnOqmztm/mMU6Iul8XbW2LravKUUH5Tp2PAPw4lE3Js4no9JfEPBcN9s/s/yK87xtUtyfOUslDg4jz8NJjJ6SjmpVsr0oeEmg5VU6rgaaF0sgTzZYMAYFaS0kn8NlP7acFaeHkkj3Fe7ftKNHgttE0bxY6kpOms8WOz2Xu62wzlEBAVF/G1R3mWK+Sd4jTNgQV/qjraxm0U16V0NpPFjgyV4ynIbX7XLOSUD4c5MH4EJWnkyM+LgDfRwc+G6GPOEYTU3beIoRK9TVPvt5UFHz7GAWHHwzBlj221j/XYDuT/W9UF5+Zaa9NM8MmTMM9mTxKnWus2p916qWE08o7 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 May 2026 19:41:51.4540 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 1f68088d-3ae9-438a-e021-08debcf12a4e 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: CH2PEPF00000140.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB8996 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260528_124200_720638_AE94D0A5 X-CRM114-Status: GOOD ( 12.76 ) 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 Wed, May 27, 2026 at 10:14:03PM +0000, Pranjal Shrivastava wrote: > Introduce a new bit flag, CMDQ_PROD_STOP_FLAG (bit 30), in the command > queue's producer index to safely gate command submissions during device > suspension. > > The flag embeds the suspend state directly into the existing global state > The flag checked in the compxchg loop in arm_smmu_cmdq_issue_cmdlist(), s/compxchg/cmpxchg > which acts as a Point of Commitment, ensuring that no indices are > reserved or committed once the SMMU begins suspending. > > This prevents a situation of "abandoned batches" where indices are > incremented but commands are never written, which would otherwise > lead to timeout during the drain poll. > > Update queue_inc_prod_n() to preserve this flag during index > calculations, ensuring that any in-flight commands that successfully > passed the point of commitment can proceed to completion while the > flag remains set. > > Suggested-by: Daniel Mentz > Signed-off-by: Pranjal Shrivastava Reviewed-by: Nicolin Chen