[PATCH v3 1/2] dt-bindings: iommu: dart: Support specifying the DMA aperture

[Janne Grunau]

Apple DARTs are often connected directly to devices that expect only a
portion of their address space to be used for DMA (for example, because
other ranges are mapped directly to something else).

Follow the "#iommu-cells = <4>" example from iommu.txt and allow
specifying the DMA aperture via additional cells. Since DART is used on
64-bit Apple silicon systems use two cells to specify the start and
length of the aperture. A common aperture starts at 0x100_0000_0000
and spans a 36-bit address space.

This corresponds to the vm-base and vm-size properties on the Apple
device tree side of things.

As not all devices require this and to keep compatibility with existing
device trees allow 1 and 5 as values for #iommu-cells.

Signed-off-by: Janne Grunau <j at jannau.net>
---
 Documentation/devicetree/bindings/iommu/apple,dart.yaml | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/Documentation/devicetree/bindings/iommu/apple,dart.yaml b/Documentation/devicetree/bindings/iommu/apple,dart.yaml
index 47ec7fa52c3a..6efbe732b4ce 100644
--- a/Documentation/devicetree/bindings/iommu/apple,dart.yaml
+++ b/Documentation/devicetree/bindings/iommu/apple,dart.yaml
@@ -44,10 +44,12 @@ properties:
       Optional since not all IOMMUs are attached to a clock gate.
 
   '#iommu-cells':
-    const: 1
+    enum: [ 1, 5 ]
     description:
-      Has to be one. The single cell describes the stream id emitted by
-      a master to the IOMMU.
+      Has to be one or five. The first cell describes the stream id emitted by
+      a master to the IOMMU. The optional second and third cell describe the
+      aperture start of a master's DMA window and fourth and fifth cell describe
+      the size of DMA window.
 
   power-domains:
     maxItems: 1
@@ -66,11 +68,11 @@ examples:
       compatible = "apple,t8103-dart";
       reg = <0x82f80000 0x4000>;
       interrupts = <1 781 4>;
-      #iommu-cells = <1>;
+      #iommu-cells = <5>;
     };
 
     master1 {
-      iommus = <&dart1 0>;
+      iommus = <&dart1 0 0x100 0x0 0x10 0x0>;
     };
 
   - |+

-- 
2.55.0