Re: [PATCH V3 5/8] dt-bindings: Add xen,grant-dma IOMMU description for xen-grant DMA ops

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On 31.05.22 14:52, Krzysztof Kozlowski wrote:

Hello Krzysztof

On 30/05/2022 23:00, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Thank you for your patch. There is something to discuss/improve.

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..ab5765c
--- /dev/null
+++ b/Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml
@@ -0,0 +1,49 @@
+# 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@xxxxxxxxxx>
+
+description:
+  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 binding is required to restrict memory access using Xen grant mappings.
+
+properties:
+  compatible:
+    const: xen,grant-dma
+
+  '#iommu-cells':
+    const: 1
+    description:
+      Xen specific IOMMU is multiple-master IOMMU device.
+      The single cell describes the domid (domain ID) of the domain where
+      the backend is running.
+
+required:
+  - compatible
+  - "#iommu-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    xen_iommu {
No underscores in node names, generic node names, so this looks like
"iommu".


ok, will change



+        compatible = "xen,grant-dma";
+        #iommu-cells = <1>;
+    };
+
+    virtio@3000 {
+        compatible = "virtio,mmio";
+        reg = <0x3000 0x100>;
+        interrupts = <41>;
+
+        /* The backend is located in Xen domain with ID 1 */
+        iommus = <&xen_iommu 1>;
There is no need usually to give consumer examples in provider binding.
If there is nothing specific here (looks exactly like every IOMMU
consumer in Linux kernel), drop the consumer.


I got it.  There is nothing specific from the device tree's perspective, I was thinking to draw attention to the IOMMU specifier (in our case, the master device's ID == backend's domain ID). But  '#iommu-cells' description above already clarifies that. Will drop.



+    };

Best regards,
Krzysztof

--
Regards,

Oleksandr Tyshchenko




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