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    SubjectRe: [PATCH v2] devicetree: Add generic IOMMU device tree bindings
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    On Wednesday 04 June 2014 14:56:01 Will Deacon wrote:
    > On Wed, Jun 04, 2014 at 02:44:03PM +0100, Thierry Reding wrote:
    > > On Fri, May 30, 2014 at 09:54:37PM +0200, Arnd Bergmann wrote:
    > > > On Friday 30 May 2014 22:29:13 Hiroshi Doyu wrote:
    > > > > The disadvantage of this is that this limits the max number of streamIDs
    > > > > to support. If # of streamID is increased later more than 64, this
    > > > > format cannot cover any more. You have to predict the max # of streamIDs
    > > > > in advance if steamID is statically assigned.
    > > > >
    > > >
    > > > Well, the iommu specific binding could allow a variable #address-cells.
    > > > That way, you just need to know the number of stream IDs for that instance
    > > > of the iommu.
    > >
    > > That sounds fairly complicated to me. I don't see what that buys us over
    > > the clarity and simplicity that the above explicit notation gives us. Is
    > > it not more common for a device to have a single master rather than a
    > > whole bunch of them?
    >
    > I've never seen a device upstream of an ARM SMMU with a single stream-id;
    > they always seem to have a whole bunch of them. Calxeda's SATA controller
    > had 10 IDs, for example, and a PL330 DMA controller tends to have at least
    > 3.

    What are those good for? Would we just always use the first one?

    Arnd


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