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Wysocki" , Thomas Gleixner , Anup Patel , Greg Kroah-Hartman , Danilo Krummrich , Manivannan Sadhasivam , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Bjorn Helgaas , Arnd Bergmann , Shuah Khan , Richard Zhu , Lucas Stach , Lorenzo Pieralisi , Rob Herring , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Krzysztof Kozlowski , Conor Dooley , Niklas Cassel , dlemoal@kernel.org, jdmason@kudzu.us, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org, linux-kselftest@vger.kernel.org, imx@lists.linux.dev, devicetree@vger.kernel.org Subject: Re: [PATCH v15 02/15] irqdomain: Add IRQ_DOMAIN_FLAG_MSI_IMMUTABLE and irq_domain_is_msi_immutable() Message-ID: References: <20250211-ep-msi-v15-0-bcacc1f2b1a9@nxp.com> <20250211-ep-msi-v15-2-bcacc1f2b1a9@nxp.com> <86plj1ovkk.wl-maz@kernel.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86plj1ovkk.wl-maz@kernel.org> X-ClientProxiedBy: PH2PEPF0000385C.namprd17.prod.outlook.com (2603:10b6:518:1::6a) To PAXPR04MB9642.eurprd04.prod.outlook.com (2603:10a6:102:240::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PAXPR04MB9642:EE_|DBAPR04MB7208:EE_ X-MS-Office365-Filtering-Correlation-Id: b05955af-0949-4b4c-2a21-08dd5a752173 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|52116014|7416014|376014|1800799024|366016|38350700014; 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Use this > > function to verify if the MSI controller is immutable. > > Why is that a requirement? Why should a driver even care? At v9, there were detail discussion about this https://lore.kernel.org/all/87v7w0s9a8.ffs@tglx/ let me summary: Host driver workflow like: 1. read address/data from shared memory (PC bar) 2. write data to address to trigger doorbell. 1 and 2 is not atomic. So EP side may call set_affinity function during 1 and 2, address/data may be changed in some MSI provider, so 2 write to previous address/data pair, which may not existed or map to other place and cause write to unexpected place. Frank > > M. > > -- > Without deviation from the norm, progress is not possible.