[PATCH v3 02/10] devicetree: Add generic IOMMU device tree bindings
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From: Will Deacon <hidden>
Date: 2014-06-27 13:55:47
Also in:
linux-devicetree, linux-iommu, linux-tegra, lkml
Hi Thierry, On Thu, Jun 26, 2014 at 09:49:42PM +0100, Thierry Reding wrote:
From: Thierry Reding <redacted>
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
Signed-off-by: Thierry Reding <redacted>[...]
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+Required properties: +-------------------- +- #iommu-cells: The number of cells in an IOMMU specifier needed to encode an + address. + +Typical values for the above include: +- #iommu-cells = <0>: Single master IOMMU devices are not configurable and + therefore no additional information needs to be encoded in the specifier. + This may also apply to multiple master IOMMU devices that do not allow the + association of masters to be configured.
A multiple-master capable IOMMU could be built with a single master, but we'd still need #iommu-cells > 0 here. I appreciate this is just an example, but the wording sounds like it's enforced.
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+- #iommu-cells = <1>: Multiple master IOMMU devices may need to be configured + in order to enable translation for a given master. In such cases the single + address cell corresponds to the master device's ID.
Again, we will definitely need more than one cell in this case, as I fully expect multiple StreamIDs for each master (e.g. Qualcomm mentioned on the list the other day that they have a master emitting 43 unique IDs). Anyway, the actual binding looks great, I just don't want people to think they need to do something different because they don't fit your example use-cases.
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+Multiple-master IOMMU: +---------------------- + + iommu { + /* the specifier represents the ID of the master */ + #iommu-cells = <1>; + }; + + master { + /* device has master ID 42 in the IOMMU */ + iommus = <&/iommu 42>; + }; + +Multiple-master IOMMU with configurable DMA window: +--------------------------------------------------- + + / { + #address-cells = <1>; + #size-cells = <1>; + + iommu { + /* master ID, address and length of DMA window */ + #iommu-cells = <4>; + }; + + master { + /* master ID 42, 4 GiB DMA window starting at 0 */ + iommus = <&/iommu 42 0 0x1 0x0>; + }; + };
Could you also please include an example of a master with multiple IDs? Will