linux-kernel - [PATCH 3/4] dt-bindings: of: Add plumbing for bounced DMA pool

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Date:   Mon, 13 Jul 2020 17:12:10 +0800
From:   Claire Chang <tientzu@...omium.org>
To:     robh+dt@...nel.org, frowand.list@...il.com, hch@....de,
        m.szyprowski@...sung.com, robin.murphy@....com
Cc:     treding@...dia.com, gregkh@...uxfoundation.org,
        saravanak@...gle.com, suzuki.poulose@....com,
        dan.j.williams@...el.com, heikki.krogerus@...ux.intel.com,
        bgolaszewski@...libre.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        tfiga@...omium.org, drinkcat@...omium.org,
        Claire Chang <tientzu@...omium.org>
Subject: [PATCH 3/4] dt-bindings: of: Add plumbing for bounced DMA pool

Introduce the new compatible string, bounced-dma-pool, for bounced DMA.
One can specify the address and length of the bounced memory region by
bounced-dma-pool in the device tree.

Signed-off-by: Claire Chang <tientzu@...omium.org>
---
 .../reserved-memory/reserved-memory.txt       | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
index 4dd20de6977f..45b3134193ea 100644
--- a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
+++ b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
@@ -51,6 +51,24 @@ 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.
+        - bounced-dma-pool: This indicates a region of memory meant to be used
+          as a pool of DMA bounce buffers for a given device. 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. Also, there must be a bounced-dma property in the
+          device node to specify the indexes of reserved-memory nodes. One can
+          specify two reserved-memory nodes in the device tree. One with
+          shared-dma-pool to handle the coherent DMA buffer allocation, and
+          another one with bounced-dma-pool for regular DMA to/from system
+          memory, which would be subject to bouncing. The main purpose for
+          bounced 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 a
+          way to restrict the DMA to a predefined memory region.
         - vendor specific string in the form <vendor>,[<device>-]<usage>
 no-map (optional) - empty property
     - Indicates the operating system must not create a virtual mapping
@@ -117,6 +135,17 @@ one for multimedia processing (named multimedia-memory@...00000, 64MiB).
 			compatible = "acme,multimedia-memory";
 			reg = <0x77000000 0x4000000>;
 		};
+
+		wifi_bounced_dma_mem_region: wifi_bounced_dma_mem_region {
+			compatible = "bounced-dma-pool";
+			reg = <0x50000000 0x4000000>;
+		};
+
+		wifi_coherent_mem_region: wifi_coherent_mem_region {
+			compatible = "shared-dma-pool";
+			reg = <0x54000000 0x400000>;
+		};
+
 	};
 
 	/* ... */
@@ -135,4 +164,11 @@ one for multimedia processing (named multimedia-memory@...00000, 64MiB).
 		memory-region = <&multimedia_reserved>;
 		/* ... */
 	};
+
+	pcie_wifi: pcie_wifi@0,0 {
+		memory-region = <&wifi_bounced_dma_mem_region>,
+			 <&wifi_coherent_mem_region>;
+		bounced-dma = <0>, <1>;
+		/* ... */
+	};
 };
-- 
2.27.0.383.g050319c2ae-goog