linux-kernel - [PATCH V4 5/8] dt-bindings: Add xen,grant-dma IOMMU description for xen-grant DMA ops

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Message-Id: <1654197833-25362-6-git-send-email-olekstysh@gmail.com>
Date:   Thu,  2 Jun 2022 22:23:50 +0300
From:   Oleksandr Tyshchenko <olekstysh@...il.com>
To:     xen-devel@...ts.xenproject.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org
Cc:     Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Rob Herring <robh+dt@...nel.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Julien Grall <julien@....org>, Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH V4 5/8] dt-bindings: Add xen,grant-dma IOMMU description for xen-grant DMA ops

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>

The main purpose of this binding is to communicate Xen specific
information using generic IOMMU device tree bindings (which is
a good fit here) rather than introducing a custom property.

Introduce Xen specific IOMMU for the virtualized device (e.g. virtio)
to be used by Xen grant DMA-mapping layer in the subsequent commit.

The reference to Xen specific IOMMU node using "iommus" property
indicates that Xen grant mappings need to be enabled for the device,
and it specifies the ID of the domain where the corresponding backend
resides. The domid (domain ID) is used as an argument to the Xen grant
mapping APIs.

This is needed for the option to restrict memory access using Xen grant
mappings to work which primary goal is to enable using virtio devices
in Xen guests.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>
---
Changes RFC -> V1:
   - update commit subject/description and text in description
   - move to devicetree/bindings/arm/

Changes V1 -> V2:
   - update text in description
   - change the maintainer of the binding
   - fix validation issue
   - reference xen,dev-domid.yaml schema from virtio/mmio.yaml

Change V2 -> V3:
   - Stefano already gave his Reviewed-by, I dropped it due to the changes (significant)
   - use generic IOMMU device tree bindings instead of custom property
     "xen,dev-domid"
   - change commit subject and description, was
     "dt-bindings: Add xen,dev-domid property description for xen-grant DMA ops"

Changes V3 -> V4:
   - add Stefano's R-b
   - remove underscore in iommu node name
   - remove consumer example virtio@...0
   - update text for two descriptions
---
 .../devicetree/bindings/iommu/xen,grant-dma.yaml   | 39 ++++++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml

diff --git a/Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml b/Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml
new file mode 100644
index 00000000..be1539d
--- /dev/null
+++ b/Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml
@@ -0,0 +1,39 @@
+# SPDX-License-Identifier: (GPL-2.0-only or BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iommu/xen,grant-dma.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Xen specific IOMMU for virtualized devices (e.g. virtio)
+
+maintainers:
+  - Stefano Stabellini <sstabellini@...nel.org>
+
+description:
+  The Xen IOMMU represents the Xen grant table interface. Grant mappings
+  are to be used with devices connected to the Xen IOMMU using the "iommus"
+  property, which also specifies the ID of the backend domain.
+  The binding is required to restrict memory access using Xen grant mappings.
+
+properties:
+  compatible:
+    const: xen,grant-dma
+
+  '#iommu-cells':
+    const: 1
+    description:
+      The single cell is the domid (domain ID) of the domain where the backend
+      is running.
+
+required:
+  - compatible
+  - "#iommu-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    iommu {
+        compatible = "xen,grant-dma";
+        #iommu-cells = <1>;
+    };
-- 
2.7.4