[PATCH v14 11/12] 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>
Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Tested-by: Will Deacon <will@xxxxxxxxxx>
---
 .../reserved-memory/reserved-memory.txt       | 36 +++++++++++++++++--
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git 
a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt 
b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
index e8d3096d922c..39b5f4c5a511 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
@@ -85,10 +102,11 @@ memory-region-names (optional) - a list of names, one for 
each corresponding
 
 Example
 -------
-This example defines 3 contiguous regions are defined for Linux kernel:
+This example defines 4 contiguous regions for Linux kernel:
 one default of all device drivers (named linux,cma@72000000 and 64MiB in size),
-one dedicated to the framebuffer device (named framebuffer@78000000, 8MiB), and
-one for multimedia processing (named multimedia-memory@77000000, 64MiB).
+one dedicated to the framebuffer device (named framebuffer@78000000, 8MiB),
+one for multimedia processing (named multimedia-memory@77000000, 64MiB), and
+one for restricted dma pool (named restricted_dma_reserved@0x50000000, 64MiB).
 
 / {
        #address-cells = <1>;
@@ -120,6 +138,11 @@ one for multimedia processing (named 
multimedia-memory@77000000, 64MiB).
                        compatible = "acme,multimedia-memory";
                        reg = <0x77000000 0x4000000>;
                };
+
+               restricted_dma_reserved: restricted_dma_reserved {
+                       compatible = "restricted-dma-pool";
+                       reg = <0x50000000 0x4000000>;
+               };
        };
 
        /* ... */
@@ -138,4 +161,11 @@ one for multimedia processing (named 
multimedia-memory@77000000, 64MiB).
                memory-region = <&multimedia_reserved>;
                /* ... */
        };
+
+       pcie_device: pcie_device@0,0 {
+               reg = <0x83010000 0x0 0x00000000 0x0 0x00100000
+                      0x83010000 0x0 0x00100000 0x0 0x00100000>;
+               memory-region = <&restricted_dma_reserved>;
+               /* ... */
+       };
 };
-- 
2.32.0.288.g62a8d224e6-goog