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Miller" , Nicolas Ferre , Alexandre Belloni , Claudiu Beznea , Koichiro Den , Niklas Cassel , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-nvme@lists.infradead.org, mhi@lists.linux.dev, linux-arm-msm@vger.kernel.org, linux-crypto@vger.kernel.org, linux-arm-kernel@lists.infradead.org, imx@lists.linux.dev Subject: Re: [PATCH v2 1/8] dmaengine: Add API to combine configuration and preparation (sg and single) Message-ID: References: <20251218-dma_prep_config-v2-0-c07079836128@nxp.com> <20251218-dma_prep_config-v2-1-c07079836128@nxp.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: SN7PR04CA0188.namprd04.prod.outlook.com (2603:10b6:806:126::13) To PA4PR04MB9366.eurprd04.prod.outlook.com (2603:10a6:102:2a9::8) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PA4PR04MB9366:EE_|OSKPR04MB11439:EE_ X-MS-Office365-Filtering-Correlation-Id: 7d2e412c-8629-4b48-5687-08de842e2ced X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|19092799006|52116014|376014|366016|56012099003|18002099003|22082099003|38350700014; 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This > > > > works well when configuration is done only once during initialization. > > > > > > > > However, in cases where the burst length or source/destination address must > > > > be adjusted for each transfer, calling two functions is verbose and > > > > requires additional locking to ensure both steps complete atomically. > > > > > > > > Add a new API dmaengine_prep_config_single() and dmaengine_prep_config_sg() > > > > and callback device_prep_config_sg() that combines configuration and > > > > preparation into a single operation. If the configuration argument is > > > > passed as NULL, fall back to the existing implementation. > > > > > > > > Add a new API dmaengine_prep_config_single_safe() and > > > > dmaengine_prep_config_sg_safe() for re-entrancy, which require driver > > > > implement callback device_prep_config_sg(). > > > > > > Okay to add API > > > > > > > + struct dma_async_tx_descriptor *(*device_prep_config_sg)( > > > > + struct dma_chan *chan, struct scatterlist *sgl, > > > > + unsigned int sg_len, enum dma_transfer_direction direction, > > > > + unsigned long flags, struct dma_slave_config *config, > > > > + void *context); > > > > > > Do we want to have drivers implement one more callback. It does not make > > > sense to me. Why not handle this in framework and have it call the > > > respective lower level APIs. > > > > To avoid use addtional lock! suppose each API is re-entriable. > > > > thread 1: call dmaengine_prep_config_sg_safe() > > thread 2: call dmaengine_prep_config_sg_safe() > > > > If DMA engine driver implement device_prep_config_sg, thread 1 and thread 2 > > can run parallel. > > > > If driver have not implement this callback, it have to use mutex make sure > > config and prep atomic. > > > > https://lore.kernel.org/dmaengine/20260109-edma_dymatic-v1-0-9a98c9c98536@nxp.com/ > > show finial opitimziation result, which depend on this. If can't call > > prep() function parallel, which will kill performace. > > Which seems to be 10% in your case. > > > > Drivers should implement simple apis and collectively the functionality > > > can come from the framework. > > > > > > Would you consider revising as such. Bonus all existing drivers can > > > start using this API, no change required for drivers in that case' > > > > Not that simple, some devices just call config at probe, especial fix > > FIFO address and burst length. > > > > Call config and prep only need for the case, which need adjust src/dst > > address, burst length or other parameter for each transfer. > > Correct. In the cases where config is done once they can invoke with > NULL config. I would like the middle layer to handle complexities and > drivers should be simpler This patches already implement these. If you don't like add new callback, how about change existing callback by add config * and update all drivers. Frank > > > > > Frank > > > > > > > > > > > -- > > > ~Vinod > > -- > ~Vinod