[PATCH V12 3/7] dma: add Qualcomm Technologies HIDMA management driver

Marc Zyngier
2016-01-15T17:32:06Z

On 15/01/16 17:16, Sinan Kaya wrote:
>>>> 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.
>
>>
>>> 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.
>
>>
>>> The mechanism used here is not different from VFIO PCI from user perspective.
>>>
>>>>
>>>> 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.

Then may I suggest you both synchronize your submissions? I'd really
like to hear from the QEMU maintainers that they are satisfied with that
side of the story as well.

Thanks,

M.
--
Jazz is not dead. It just smells funny...