On 6/24/2014 11:11 AM, Will Deacon wrote:

On Tue, Jun 24, 2014 at 06:57:44PM +0100, Olav Haugan wrote:

quoted

On 6/24/2014 2:18 AM, Will Deacon wrote:

quoted

On Sat, Jun 21, 2014 at 12:16:25AM +0100, Olav Haugan wrote:

quoted

We have multiple-master SMMUs and each master emits a variable number of
StreamIDs. However, we have to apply a mask (the ARM SMMU spec allows
for this) to the StreamIDs due to limited number of StreamID 2 Context
Bank entries in the SMMU. If my understanding is correct we would
represent this in the DT like this:

	iommu {
		#address-cells = <2>;
		#size-cells = <0>;
	};

	master@a {
		...
		iommus = <&iommu StreamID0 MASK0>,
			 <&iommu StreamID1 MASK1>,
			 <&iommu StreamID2 MASK2>;
	};

Stupid question, but why not simply describe the masked IDs? What use does
the `raw' ID have to Linux?

We do describe the masked StreamID (SID) but we need to specify the mask
that the SMMU should apply to the incoming SIDs, right?

We have a bus master that emits 43 unique SIDs. However, we have only 40
SMMU_SMRn registers in the SMMU. So we need to mask out some of the
incoming SID bits so that the 43 SIDs can match one of 40 entries in the
SMR.

Hmm, so you're talking about stream matching, right? That doesn't belong in
the device-tree. I appreciate that the current driver does a terrible job at
allocating the SMRs (it's bloody difficult!), but we should try to improve
the dynamic behaviour instead of moving configuration of the SMMU out into
device-tree, where it's inflexible at best.

I am talking about SMMU_SMRn[MASK] register bits. This is not something
that can be dynamically detected at run-time. It is configuration at the
same level as the actual StreamIDs.

Thanks,


Olav Haugan

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