On 06/26/2014 02:49 PM, Thierry Reding wrote: > From: Thierry Reding <treding@xxxxxxxxxx> > > This commit introduces a generic device tree binding for IOMMU devices. > Only a very minimal subset is described here, but it is enough to cover > the requirements of both the Exynos System MMU and Tegra SMMU as > discussed here: > > https://lkml.org/lkml/2014/4/27/346 > diff --git a/Documentation/devicetree/bindings/iommu/iommu.txt b/Documentation/devicetree/bindings/iommu/iommu.txt > +When an "iommus" property is specified in a device tree node, the IOMMU will > +be used for address translation. If a "dma-ranges" property exists in the > +device's parent node it will be ignored. An exception to this rule is if the > +referenced IOMMU is disabled, in which case the "dma-ranges" property of the > +parent shall take effect. I wonder how useful that paragraph is. The fact that someone disabled a particular IOMMU's node doesn't necessarily mean that the HW can actually do that; an IOMMU might always be active in HW and always translate accesses by some master. In that case, the fallback to dma-ranges wouldn't correlate with what the HW actually does. Perhaps all we need is to add a note to that effect here? -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
