Re: [PATCH] documentation: iommu: add description of ARM System MMU binding

[Olav Haugan <ohaugan@codeaurora.org>]

Hi Will,

On 4/24/2013 2:55 AM, Will Deacon wrote:
> On Tue, Apr 23, 2013 at 11:54:53PM +0100, Olav Haugan wrote:
>> On 4/18/2013 12:01 PM, Will Deacon wrote:
> Getting phandles has no dependencies on anything -- the only dependency is
> that the device is added to the bus on which the SMMU sits, just like every
> other IOMMU driver.
> 
>>> Why would a page table shared between devices require multiple context
>>> banks? Multiple SMRs and S2CRs, sure, but they would ultimately point at the
>>> same context bank (and hence same address space).
>>
>> What if you want to have 2 different VMID's being generated? Also, what
>> about TLB management? If I have two context banks I can invalidate only
>> entries associated with 1 of the context banks (if VMID differ for the
>> two context banks).
> 
> Huh? We allocate one VMID per domain. If you want more VMIDs, use more
> domains. TLB invalidation is per-domain, so there's no issue there.

If we allocate a new domain you would have another address space (page
table), no? I was just trying to figure out if your binding proposal
would allow for 2 context banks in one domain which it does not seem to
support.

>>> If a master needs to be in two address spaces at once, then it will need to
>>> attach it's StreamIDs to different domains. You can't place a single
>>> StreamID in two address spaces (this is an architectural constraint).
>>
>> Yes, you would have a separate domain. I am just wondering how I would
>> model this in DT using the bindings that you are proposing? How does it
>> work? The bindings specify bus masters to StreamIDs. So if I call attach
>> with the master device you will allocate a context bank and program the
>> StreamIDs as specified in the DT. So now if I want to have another
>> context bank associated with the same master device what do I do? I call
>> into attach with a new domain but with the same master device but the
>> master device is already attached to a context/domain.
> 
> Why would you want to place a StreamID into two domains? That doesn't make
> any sense and isn't even supported by the architecture (things like
> conflicting SMR entries may not even be reported).

I think you misunderstood me. I am talking about having for example 1
master with two (2) context banks so that StreamID "1" goes to CB0 and
StreamID "2" goes to CB1. This means that the master device is attached
to two different domains. How do I model this with the the device tree
bindings?



Olav Haugan

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