On 09/07/15 02:56, leizhen wrote:
[...]
@@ -1928,9 +1929,35 @@ static int arm_smmu_of_xlate(struct device *dev, struct
of_phandle_args *args)
[...]
+ for (i = 0; i < args->args_count; i++) {
I'm dubious of the value of looping here - having n>1 #iommu-cells per phandle
means that every platform device behind one SMMU must have the same number of
stream IDs, or you still have to have
repeated phandles for every device with some greater multiple of n stream IDs
each, but ruling out any device with <n. I'm not sure how realistic that is,
and whether there's any real benefit beyond
saving a handful of bytes in the DTB.
As you mentioned before, a master with two streamIDs can be written as
below(This is also mentioned in
Documentation\devicetree\bindings\iommu\iommu.txt):
#iommu-cells = <1>;
iommus = <&{/iommu} 23>, <&{/iommu} 24>;
On my hardware platform, a master only have one streamID. But I tested two
cases:
#iommu-cells = <1>;
1. iommus = <&smmu0 good-sid>, <&smmu0 bad-sid>;
2. iommus = <&smmu0 bad-sid>, <&smmu0 good-sid>;
All of these two cases worked well.
Well, if each master contains two streamIDs(or more but equal), this for loop
is needed.
My point is that args_count == #iommu-cells here. If you mandate
#iommu-cells == 1 as per your example (which in my opinion *is* the
right thing to do), then looping over something which is guaranteed to
be a single item is pointless.
You'd only need the loop if args_count > 1, for example:
#iommu-cells = <2>;
1: iommus = <&smmu0 sid1 sid2>;
2: iommus = <&smmu0 sid1 sid2>, <&smmu0 sid3 sid4>;
but then you'd be also stuck describing any device with an odd number of
stream IDs on that SMMU:
3: iommus = <&smmu0 sid1 what-do-I-put-here?>;
which is why I don't think it's worth trying to accommodate anything
other than #iommu-cells == 1, and for that case you know you will only
ever have to deal with args[0] in each of_xlate() call.
Robin.
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