schemas: iommu: Add "iommu-ranges" on a device node - #207
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When "iommu-addresses" is the only property being described and there is no backing "reg" (i.e. no actual reserved system memory), it does not belong under /reserved-memory. A device's IOVA range is specific to how that device's own address space is mapped, not a description of memory shared across the system. So "iommu-addresses" should only be used with a "reg"; only then should it be placed inside the /reserved-memory. IOVA addresses specific to a particular device should instead go under that device's own node. This was discussed here: https://lore.kernel.org/all/662f7093-fb0a-4564-9ca0-98e03e68ba9a@kernel.org Using the same "iommu-addresses" property, typed as a phandle array, under the device's own node is not suitable, because "iommu-addresses" expects a phandle. If the property is placed inside the device node, a phandle is not required, since the property then belongs only to that device node. Introduced a new property, "iommu-ranges", for the IOVA ranges required for DMA memory mapping to that device node. If a device is restricted to use only specific IOVA regions for DMA memory mapping, "iommu-ranges" should be present on that device's node, listing those usable ranges. If a device has no such restriction, "iommu-ranges" is not needed, and the device's full IOVA address space remains available for DMA memory mapping. Suggested-by: Rob Herring <robh@kernel.org> Signed-off-by: Vishnu Reddy <busanna.reddy@oss.qualcomm.com>
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When "iommu-addresses" is the only property being described and there is no backing "reg" (i.e. no actual reserved system memory), it does not belong under /reserved-memory. A device's IOVA range is specific to how that device's own address space is mapped, not a description of memory shared across the system. So "iommu-addresses" should only be used with a "reg"; only then should it be placed inside the /reserved-memory. IOVA addresses specific to a particular device should instead go under that device's own node. This was discussed here:
https://lore.kernel.org/all/662f7093-fb0a-4564-9ca0-98e03e68ba9a@kernel.org
Using the same "iommu-addresses" property, typed as a phandle array, under the device's own node is not suitable, because "iommu-addresses" expects a phandle. If the property is placed inside the device node, a phandle is not required, since the property then belongs only to that device node. Introduced a new property, "iommu-ranges", for the IOVA ranges required for DMA memory mapping to that device node.
If a device is restricted to use only specific IOVA regions for DMA memory mapping, "iommu-ranges" should be present on that device's node, listing those usable ranges. If a device has no such restriction, "iommu-ranges" is not needed, and the device's full IOVA address space remains available for DMA memory mapping.
Suggested-by: Rob Herring robh@kernel.org
Signed-off-by: Vishnu Reddy busanna.reddy@oss.qualcomm.com