Re: [PATCH v12 11/12] dt-bindings: of: Add restricted DMA pool

On Wed, 16 Jun 2021, Claire Chang wrote:

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@chromium.org

.../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..46804f24df05 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_mem_reserved>;
  

Shouldn't it be &restricted_dma_reserved ?