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SubjectRe: [RFC PATCH 2/2] iommu: rockchip: Handle system-wide and runtime PM
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Hi Kevin,

On Friday 19 December 2014 03:27:35 Rafael J. Wysocki wrote:
> On Thursday, December 18, 2014 11:28:58 PM Laurent Pinchart wrote:
> > Hi Kevin,
>
> [cut]
>
>>>>> It would be better to be able to reference count the DMA engine from
>>>>> the bus master IMO and arguably you can use the runtime PM framework
>>>>> for that. Namely, give bus masters someting like
>>>>>
>>>>> pm_runtime_get_my_DMA_engine(bus_master_device)
>>>>> pm_runtime_put_my_DMA_engine(bus_master_device)
>>>>>
>>>>> and let them call these as they see fit.
>>>>
>>>> Please note that we're not talking about DMA engines here, but about
>>>> IOMMUs. DMA is involved through the DMA mapping API which hides the
>>>> IOMMU completely from the bus master drivers, not the DMA engine API.
>>>>
>>>> Exposing the IOMMU is something we want to avoid, but DMA mapping
>>>> start/stop operations could certainly be implemented.
>>>
>>> The problem with that is it only solves the IOMMU problem. We have a
>>> more generic PM dependency problem of which this IOMMU example is only a
>>> subset, so I think we need a more generic solution.
>>
>> I agree that a more generic solution is needed at least to support ACPI
>> _DEP, but that might not be optimal in the IOMMU use case as explained
>> above.
>
> Well, since we need it anyway, why don't we implement it and then figure out
> if anything more specific needs to be done for the IOMMU case?

Patches are welcome ;-)

--
Regards,

Laurent Pinchart



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