Re: Question about arm smmu

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

On Wed, Nov 04, 2015 at 09:44:40PM +0800, Peng Fan wrote:
> Hi Will,

Hello,

> I am trying to enable SMMU(mmu500) on an platform.
> My platform support only 32 SIDs, but it have more than 100 masters.
> So I need to let different masters share one SID. I read current
> arm-smmu.c, but it needs each master has unique SID. Do you have
> some suggestions about how to let different masters sharing one
> SID?

We can achieve that using iommu_groups, but then we need a way to
describe those groups in the device-tree, as opposed to putting
each device into its own group like we do at present. Robin (CC'd) had
some work-in-progress for this, iirc.

> On my platform, SID can be dynamically programmed. So I can program
> DMA0 and DMA1 using one SID, saying 0x5. But I do not have a good
> idea how to support this use case in arm-smmu.c driver.

I think we've have the firmware allocating the SIDs, then describing
the grouping to Linux in the device-tree.

Will