linux-kernel - Re: [PATCH RFC 0/2] iommu/arm-smmu-v3: bypass streamid zero on i.MX95

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Message-ID: <a8c42a6c-bac3-4ebc-8a29-e6c0ed4567c3@arm.com>
Date: Tue, 15 Oct 2024 15:47:05 +0100
From: Robin Murphy <robin.murphy@....com>
To: "Peng Fan (OSS)" <peng.fan@....nxp.com>, Will Deacon <will@...nel.org>,
 Joerg Roedel <joro@...tes.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Cc: Joy Zou <joy.zou@....com>, linux-arm-kernel@...ts.infradead.org,
 iommu@...ts.linux.dev, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Peng Fan <peng.fan@....com>,
 Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH RFC 0/2] iommu/arm-smmu-v3: bypass streamid zero on i.MX95

On 2024-10-15 4:14 am, Peng Fan (OSS) wrote:
> i.MX95 eDMA3 connects to DSU ACP, supporting dma coherent memory to
> memory operations. However TBU is in the path between eDMA3 and ACP,
> need to bypass the default SID 0 to make eDMA3 work properly.

I'm confused, why not just describe that the device owns this StreamID 
in the DT the normal way, i.e, "iommus = <&smmu 0>;"?

Thanks,
Robin.

> I was also thinking to introduce "bypass-sids = <0xA 0xB 0xC ...>" to
> make this reusable for others, but not sure. I could switch to
> "bypass-sids" if you prefer.
> 
> Signed-off-by: Peng Fan <peng.fan@....com>
> ---
> Peng Fan (2):
>        dt-bindings: iommu: arm,smmu-v3: introduce nxp,imx95-bypass-sid-zero
>        iommu/arm-smmu-v3: Bypass SID0 for NXP i.MX95
> 
>   .../devicetree/bindings/iommu/arm,smmu-v3.yaml        |  4 ++++
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c           | 19 ++++++++++++++++---
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h           |  1 +
>   3 files changed, 21 insertions(+), 3 deletions(-)
> ---
> base-commit: d61a00525464bfc5fe92c6ad713350988e492b88
> change-id: 20241014-smmuv3-120b24bc4659
> 
> Best regards,