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

[Peng Fan]

Hi Robin,

> 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>;"?

Current SMMU-v3 driver not support streamID sharing, but we have
limited streamIDs(i.MX95 max supports 64 SIDs). However the eDMA
supports 64 channels, each channel may have a SID, but not supported
by current smmuv3 driver.

We see smmu would degrade the performance in somecases, so
we wanna to give user an option to bypass SMMU for eDMA.

Thanks,
Peng.

> 
> 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@xxxxxxx>
> > ---
> > 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,