[PATCH v3 1/3] dt-bindings: arm-smmu: Document nvidia,memory-controller property

Thierry Reding
2022-04-29T08:22:58Z

On NVIDIA SoC's the ARM SMMU needs to interact with the memory
controller in order to map memory clients to the corresponding stream
IDs. Document how the nvidia,memory-controller property can be used to
achieve this.

Note that this is a backwards-incompatible change that is, however,
necessary to ensure correctness. Without the new property, most of the
devices would still work but it is not guaranteed that all will.

Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
---
Changes in v2:
- clarify why the new nvidia,memory-controller property is required

.../devicetree/bindings/iommu/arm,smmu.yaml | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
index da5381c8ee11..44606ad5aa39 100644
--- a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
+++ b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
@@ -157,6 +157,17 @@ properties:
power-domains:
maxItems: 1

+ nvidia,memory-controller:
+ description: |
+ A phandle to the memory controller on NVIDIA Tegra186 and later SoCs.
+ The memory controller needs to be programmed with a mapping of memory
+ client IDs to ARM SMMU stream IDs.
+
+ If this property is absent, the mapping programmed by early firmware
+ will be used and it is not guaranteed that IOMMU translations will be
+ enabled for any given device.
+ $ref: /schemas/types.yaml#/definitions/phandle
+
required:
- compatible
- reg
@@ -179,6 +190,12 @@ allOf:
reg:
minItems: 1
maxItems: 2
+
+ # The reference to the memory controller is required to ensure that the
+ # memory client to stream ID mapping can be done synchronously with the
+ # IOMMU attachment.
+ required:
+ - nvidia,memory-controller
else:
properties:
reg:
--
2.35.1