On 2021-06-03 13:24, Peter Geis wrote:
On Thu, Jun 3, 2021 at 8:07 AM Robin Murphy <[email protected]> wrote:
On 2021-05-27 03:37, [email protected] wrote:
Hi all,
I have a SoC integrate with two different types of iommus, one is ARM SMMU,
serves the PCIe/SATA/USB,
the others are vendor specific iommus, serves display device and multimedia
device.
In the current linux kernel, the iommu framework seems only support one type
iommu at runtime, if enable both types iommu, only one type can work.
Is there any way to support this kind of SoC?
Hooray! I've been forecasting this for years, but the cases we regularly
hit with internal FPGA prototyping (nor the secret unused MMU-400 I
found on RK3288) have never really been a strong enough argument to
stand behind.
Based on what I remember from looking into this a few years ago,
converting *most* of the API to per-device ops (now via dev->iommu) is
trivial; the main challenge will be getting the per-device data
bootstrapped in iommu_probe_device(), which would probably need to rely
on the fwspec and/or list of registered IOMMU instances.
The other notable thing which will need to change is the domain
allocation interface, but in practice I think everyone who calls
iommu_domain_alloc() today is in fact doing so for a specific device, so
I don't think it's as big a problem as it might first appear.
Robin.
Good Morning Robin,
I think the Tegra group would also be interested in this work.
AFAIK they have the smmu and the tegra gart and have been trying to
figure out the runtime handover from the bootloader to the kernel
without smashing everything and starting over.
No, handoff of live DMA from the bootlader is an entirely unrelated
issue, and there are already several patchsets in flight to address
various parts of that. My understanding of Tegras is that they *either*
use tegra-gart, tegra-smmu, or arm-smmu depending on the SoC generation,
but they aren't mixed within any single SoC.
Robin.
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