quoted

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This doesn't seem to tie into KVM or VFIO, and as far as I can tell
there's no mechanism for associating channels with a particular virtual
address space (i.e. no configuration of an external or internal IOMMU),
nor pinning of guest pages to allow for DMA to occur safely.

I'm using VFIO platform driver for this purpose. VFIO platform driver is 
capable of assigning any platform device to a guest machine with this driver. 

Typically VFIO-platform also comes with a corresponding reset driver.
You don't need one?

The HIDMA channel driver resets the channel before using it. That's why, I never
bothered with writing a reset driver on the hypervisor.

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You just unbind the HIDMA channel driver from the hypervisor and bind to vfio
driver using the very same approach you'd use with PCIe. 

Of course, this all assumes the presence of an IOMMU driver on the system. VFIO
driver uses the IOMMU driver to create the mappings. 

No IOMMU was described in the DT binding. It sounds like you'd need an
optional (not present in the guest) iommus property per-channel

You are right. I missed that part. I'll update the device-tree binding documentation.

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The mechanism used here is not different from VFIO PCI from user perspective.

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Given that, I'm at a loss as to how this would be used in a hypervisor
context. What am I missing?

Are there additional patches, or do you have some userspace that works
with this in some limited configuration?

No, these are the only patches. We have one patch for the QEMU but from kernel
perspective this is it. 

Do you have a link to that? Seeing it would help to ease my concerns.

The QEMU driver has not been posted yet. As far as I know, it just discovers the memory
resources on the platform object and creates mappings for the guest machine only. 

Shanker Donthineni and Vikram Sethi will post the QEMU patch later.

Thanks,
Mark.

-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project