[lkml]   [2014]   [Dec]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC PATCH 2/2] iommu: rockchip: Handle system-wide and runtime PM
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 ;-)


Laurent Pinchart

 \ /
  Last update: 2014-12-20 20:41    [W:0.069 / U:0.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site