[PATCH v3 4/8] dt-bindings: reserved-memory: Add lendable-dma-pool

[Vincent Donnefort <vdonnefort@google.com>]

Add bindings for the "lendable-dma-pool" reserved-memory CMA pool, used
to dynamically unmap pages from the kernel direct map before lending
them to a secure world.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
---
 .../reserved-memory/lendable-dma-pool.yaml    | 58 +++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/reserved-memory/lendable-dma-pool.yaml

diff --git a/Documentation/devicetree/bindings/reserved-memory/lendable-dma-pool.yaml b/Documentation/devicetree/bindings/reserved-memory/lendable-dma-pool.yaml
new file mode 100644
index 000000000000..0b924d941b4d
--- /dev/null
+++ b/Documentation/devicetree/bindings/reserved-memory/lendable-dma-pool.yaml
@@ -0,0 +1,58 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/reserved-memory/lendable-dma-pool.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: /reserved-memory Lendable DMA Pool
+
+maintainers:
+  - Vincent Donnefort <vdonnefort@google.com>
+
+description: |
+  This indicates a region of memory meant to be used as a pool of DMA buffers
+  that can be dynamically unmapped from the kernel direct map (e.g. before
+  lending to a secure world such as via Arm FF-A).
+
+  On architectures where the direct map cannot be arbitrarily modified at
+  runtime (such as arm64 without BBML3 or without rodata=full), the operating
+  system ensures this pool is mapped using last-level (PTE) page table entries.
+
+  The reusable property must be set, and no-map must not be set.
+
+allOf:
+  - $ref: reserved-memory.yaml
+
+properties:
+  compatible:
+    const: lendable-dma-pool
+
+  linux,cma-default:
+    type: boolean
+    description: >
+      If this property is present, then Linux will use the region for
+      the default pool of the contiguous memory allocator.
+
+  no-map: false
+
+required:
+  - compatible
+  - reusable
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    reserved-memory {
+        #address-cells = <1>;
+        #size-cells = <1>;
+        ranges;
+
+        linux,cma {
+            compatible = "lendable-dma-pool";
+            reusable;
+            size = <0x4000000>;
+            alignment = <0x200000>;
+            linux,cma-default;
+        };
+    };
-- 
2.56.0.542.g3ef89b7020-goog