[PATCH v7 14/15] dt-bindings: of: Add restricted DMA pool

[Claire Chang <tientzu@xxxxxxxxxxxx>]

Introduce the new compatible string, restricted-dma-pool, for restricted
DMA. One can specify the address and length of the restricted DMA memory
region by restricted-dma-pool in the reserved-memory node.

Signed-off-by: Claire Chang <tientzu@xxxxxxxxxxxx>
---
 .../reserved-memory/reserved-memory.txt       | 27 +++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git 
a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt 
b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
index e8d3096d922c..284aea659015 100644
--- a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
+++ b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
@@ -51,6 +51,23 @@ compatible (optional) - standard definition
           used as a shared pool of DMA buffers for a set of devices. It can
           be used by an operating system to instantiate the necessary pool
           management subsystem if necessary.
+        - restricted-dma-pool: This indicates a region of memory meant to be
+          used as a pool of restricted DMA buffers for a set of devices. The
+          memory region would be the only region accessible to those devices.
+          When using this, the no-map and reusable properties must not be set,
+          so the operating system can create a virtual mapping that will be 
used
+          for synchronization. The main purpose for restricted DMA is to
+          mitigate the lack of DMA access control on systems without an IOMMU,
+          which could result in the DMA accessing the system memory at
+          unexpected times and/or unexpected addresses, possibly leading to 
data
+          leakage or corruption. The feature on its own provides a basic level
+          of protection against the DMA overwriting buffer contents at
+          unexpected times. However, to protect against general data leakage 
and
+          system memory corruption, the system needs to provide way to lock 
down
+          the memory access, e.g., MPU. Note that since coherent allocation
+          needs remapping, one must set up another device coherent pool by
+          shared-dma-pool and use dma_alloc_from_dev_coherent instead for 
atomic
+          coherent allocation.
         - vendor specific string in the form <vendor>,[<device>-]<usage>
 no-map (optional) - empty property
     - Indicates the operating system must not create a virtual mapping
@@ -120,6 +137,11 @@ one for multimedia processing (named 
multimedia-memory@77000000, 64MiB).
                        compatible = "acme,multimedia-memory";
                        reg = <0x77000000 0x4000000>;
                };
+
+               restricted_dma_mem_reserved: restricted_dma_mem_reserved {
+                       compatible = "restricted-dma-pool";
+                       reg = <0x50000000 0x400000>;
+               };
        };
 
        /* ... */
@@ -138,4 +160,9 @@ one for multimedia processing (named 
multimedia-memory@77000000, 64MiB).
                memory-region = <&multimedia_reserved>;
                /* ... */
        };
+
+       pcie_device: pcie_device@0,0 {
+               memory-region = <&restricted_dma_mem_reserved>;
+               /* ... */
+       };
 };
-- 
2.31.1.751.gd2f1c929bd-goog