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charset=UTF-8 Date: Sat, 03 Oct 2026 10:51:52 +0900 Message-Id: Cc: "Danilo Krummrich" , "Gary Guo" , "Robin Murphy" , , , , , , , , , , , , Subject: Re: [PATCH 2/2] rust: scatterlist: honor the device's maximum segment size From: "Alexandre Courbot" To: "Matteo Kloiber" References: <20260831233215.287881-1-kernel@matt3o12.de> <20260831233215.287881-3-kernel@matt3o12.de> <20260913210806.125589-1-kernel@matt3o12.de> <20260927224446.1053037-1-kernel@matt3o12.de> In-Reply-To: X-ClientProxiedBy: TYCP286CA0289.JPNP286.PROD.OUTLOOK.COM (2603:1096:400:3c8::14) To MW4PR12MB6873.namprd12.prod.outlook.com (2603:10b6:303:20c::17) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW4PR12MB6873:EE_|SJ2PR12MB9210:EE_ X-MS-Office365-Filtering-Correlation-Id: 67f6d5f1-0fc4-46e3-83c3-08df20f0e6c0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|1800799024|366016|10070799003|7416014|376014|6133799003|22082099003|18002099003|10067099003|3023799007|4143699003|56012099006|11063799006; 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That being said, I think we can do both with this change. >> >> The key change here is that we introduce a structure that defines dma >> parameters for a device. This structure deliberately has no default >> implementation and new fields should be added even if they require chang= es for >> all dma drivers. > <...> > > Thanks for the detailed plan; I think it mostly makes sense. > > A few details that we have discussed offline with Danilo: > > - The `probe` methods should not take the `dma::Setup` token directly, > but rather a bus-specific struct that contains it and can be augmented > with other capabilities. Drivers would have to deconstruct it using > the `..` operator to make sure code doesn't break if we add new tokens > to it. > - The token should not assume default parameters and only call functions > corresponding to parameters explicitly set; converting the token to a > handler means the driver acknowledged all the settings, so we should > not make any parameter mandatory (the doc should of course detail what > drivers *should* do). > > With that and your plan I believe you have a solid basis to send a > RFC/PoC. :) Stumbled upon the notes I took while discussing with Danilo so sharing the extra info that was there: - As a consequence of this, the `DmaDevice` trait is likely to go away. - The name of the capabilities struct is not clear yet, but something like `pci::InitTokens` could work (because it would only contain such tokens that reference the device).