On Sun, Jun 01, 2014 at 10:55:46AM +0100, Will Deacon wrote: > On Fri, May 30, 2014 at 08:54:37PM +0100, Arnd Bergmann wrote: > > On Friday 30 May 2014 22:29:13 Hiroshi Doyu wrote: > > > Tegra,SMMU has a similar problem and we have used a fixed size bitmap(64 > > > bit) to afford 64 stream IDs so that a single device can hold multiple > > > IDs. If we apply the same bitmap to the above exmaple: > > > > > > iommu { > > > /* the specifier represents the ID of the master */ > > > #address-cells = <1>; > > > #size-cells = <0>; > > > }; > > > > > > master@a { > > > ... > > > iommus = <&smmu (BIT(1) | BIT(2) | BIT(3))>; # IDs 1 2 3 > > > }; > > > > > > master@b { > > > ... > > > iommus = <&smmu BIT(4)>; # ID 4 > > > }; > > > > > > 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. > > In general, though, the SMMU will be able to support a large number of > stream IDs (say a 16-bit space). The restriction we're interested in here is > how many different stream IDs can be emitted by a single master device > coming into the SMMU. *That* is a property of the master, not the SMMU. > > In the current arm,smmu binding I have a #stream-id-cells property in each > master. I can then feed that straight into of_parse_phandle_with_args to > enumerate the IDs for that master. The problem with that is we're > artificially restricted by MAX_PHANDLE_ARGS. Maybe I don't fully understand, but since we leave it up to the IOMMU binding to define the exact meaning of #iommu-cells, can't you simply use that to your advantage and define something like: iommus = <&smmu 0 7>; to mean IDs 0 to 7 for this particular IOMMU type? Thierry
Attachment:
pgp2pQU990W9L.pgp
Description: PGP signature