Re: [PATCHv3 14/19] iommu/tegra: smmu: Get "nvidia,memory-clients" from DT

[Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>]

On Thu, Oct 31, 2013 at 07:13:01PM +0000, Stephen Warren wrote:
> On 10/31/2013 12:02 PM, Will Deacon wrote:
> > On Thu, Oct 31, 2013 at 05:40:29PM +0000, Mark Rutland wrote:
> >> For the ARM SMMU binding, each device has a #stream-id-cells property
> >> describing how many IDs it has, and then the SMMU node has a phandle+args
> >> linkage to each of the devices attached to it, describing their stream IDs.
> >> While this does have some limitations (a device can't be plugged into multiple
> >> SMMUs with a different number of IDs), it seems generally sane.
> > 
> > If a device masters through two separate SMMUs, I think you need to describe
> > it as two devices. Even if you could describe the thing in DT, the Linux
> > driver/iommu model will quickly fall over.
> 
> Isn't that an internal Linux driver model issue? If there's a single
> logical HW block, it seems like it should have a single DT node. The
> fact that the DT node then somehow needs to instantiate two struct
> device objects within Linux seems like it shouldn't influence the DT design.

Sure, I was just pointing out that you're going to need two struct devices
for that scenario, which isn't how things would work in Linux today.

Will