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Fri, 25 Sep 2026 01:45:36 +0000 Date: Fri, 25 Sep 2026 09:43:10 +0800 From: Peng Fan To: "Rob Herring (Arm)" Cc: Frank Li , linux-kernel@vger.kernel.org, Krzysztof Kozlowski , Conor Dooley , imx@lists.linux.dev, devicetree@vger.kernel.org, Peng Fan , dmaengine@vger.kernel.org, Vinod Koul , Frank Li Subject: Re: [PATCH 1/2] dt-bindings: dma: fsl,edma: add iommu-map property Message-ID: References: <20260916-edma-iommu-v1-0-e1731968081e@nxp.com> <20260916-edma-iommu-v1-1-e1731968081e@nxp.com> <179028698602.1895482.8450136905176032994.robh@kernel.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <179028698602.1895482.8450136905176032994.robh@kernel.org> X-ClientProxiedBy: SI1PR02CA0002.apcprd02.prod.outlook.com (2603:1096:4:1f7::16) To AM8PR04MB7874.eurprd04.prod.outlook.com (2603:10a6:20b:24d::9) Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: AM8PR04MB7874:EE_|DU4PR04MB10646:EE_ X-MS-Office365-Filtering-Correlation-Id: 81d6278c-cb6d-4ff0-566a-08df1aa6b242 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|19092799006|23010399003|376014|366016|1800799024|10067099003|22082099003|56012099006|11063799006|4143699003|18002099003; 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This enables IOMMU translation for individual >> eDMA channels, where paired channels can share the same stream ID and >> channels without an entry operate in bypass mode. >> >> Also add a new example using fsl,imx95-edma5 that demonstrates the >> iommu-map usage with per-channel mappings. >> >> Assisted-by: Claude:claude-opus-4-6 >> Signed-off-by: Peng Fan >> --- >> .../devicetree/bindings/dma/fsl,edma.yaml | 89 ++++++++++++++++++++++ >> 1 file changed, 89 insertions(+) >> > >Reviewed-by: Rob Herring (Arm) Thanks for reviewing this patchset. I think I need to drop this patchset and use the other method. in https://lore.kernel.org/all/20260917144804.GI3196566@ziepe.ca/, Jason Gunthorpe does not agree to use iommu-map for eDMA channels. "The DT modeling for devices that have multiple stream-IDs is to list them all in iommus list." More comments about QCOM VPU in https://lore.kernel.org/linux-iommu/20260618151745.GD231643@ziepe.ca/ " In Linux if you use DT iommus the SW sets things up so every stream shares the same translation. If your driver/device doesn't like that there is no SW way to opt out of sharing. I think that is the first core issue that VPU was struggling with. If you have one "device" then I would argue the DT should describe all its streams using iommus in the normal way. The introduction of iommu-map for VPU is only being done because that is a convenient hack to allow Linux to unbundle the streams. It would be much harder to unbunble the streams directly from the DT iommus property, but that would probably be the cleanest, software agnostic, DT modeling. So, if we are going to do a hack in DT to accomodate Linux, I argue to choose explicit child devices so VPU does not need to create a special bus, call of_dma_configue, or hack in new DMA API things that only it will ever use. Then the explicit children can properly describe how the HW decodes IOVA into each streams in the DT (which sounds very much like a HW property to me) so that Linux produces IOVA that the HW mangling properly routes to the expected stream. Then the VPU driver just has to assemble itself from many struct devices, which I admit is also a troublesome task. " Thanks Peng > >