On Thu, Oct 31, 2013 at 08:18:08AM +0000, Hiroshi Doyu wrote:
> Stephen Warren <swarren@xxxxxxxxxxxxx> wrote @ Wed, 30 Oct 2013 23:44:04 +0100:
>
> > > + host1x {
> > > + compatible = "nvidia,tegra30-host1x", "simple-bus";
> > > + nvidia,memory-clients = <&smmu TEGRA_SWGROUP_HC>;
> > > + ....
> > > + gr3d {
> > > + compatible = "nvidia,tegra30-gr3d";
> > > + nvidia,memory-clients = <&smmu TEGRA_SWGROUP_NV
> > > + TEGRA_SWGROUP_NV2>;
> >
> > Why one cell for the host1x property, and two cells for the gr3d
> > property; shouldn't they be the same length?
>
> That can vary. Even a single device node in DT can belong to multiple
> software groups.
Same with ARM SMMU.
>
> > > diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> >
> > > +static u64 smmu_of_get_memory_client(struct device *dev)
> >
> > > + np = of_parse_phandle(dev->of_node, propname, 0);
> > > + if (np != smmu_handle->dev->of_node)
> > > + return ~0;
> > > +
> > > + prop = of_get_property(dev->of_node, propname, &bytes);
> > > + if (!prop || !bytes)
> > > + return ~0;
> >
> > of_parse_phandle_with_fixed_args() might be a good fit here, or perhaps
> > require a property #smmu-cells in the SMMU node, thus allowing the
> > non-fixed-length of_parse_phandle_with_args() to be used here.
>
> I once considered of_parse_phandle_with_args() but I couldn't use that
> since "#smmu-cells" needed to be fixed in smmu node, not in client
> node. In this case, the number of argument(number of swgroup IDs)
> varies per client device.
For the ARM SMMU binding, each device has a #stream-id-cells property
describing how many IDs it has, and then the SMMU node has a phandle+args
linkage to each of the devices attached to it, describing their stream IDs.
While this does have some limitations (a device can't be plugged into multiple
SMMUs with a different number of IDs), it seems generally sane.
Thanks,
Mark.
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