On Wed, Oct 16, 2024 at 12:56:54AM +0000, Peng Fan wrote: > > 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. If it's a system-wise global need, adding "iommu.passthrough=y" to the bootargs string should work for all trusted devices. And particular group can be changed to the IDENTITY domain too upon cmdline setting, e.g. echo identity | sudo tee /sys/class/pci_bus/0009\:01/device/iommu_group/type Thanks Nicolin
