Re: [PATCH v9 1/5] dt-bindings: reserved-memory: Document iommu-addresses

Robin Murphy
2022-10-07T13:46:28Z

On 2022-09-23 13:35, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
>
> This adds the "iommu-addresses" property to reserved-memory nodes, which
> allow describing the interaction of memory regions with IOMMUs. Two use-
> cases are supported:
>
> 1. Static mappings can be described by pairing the "iommu-addresses"
> property with a "reg" property. This is mostly useful for adopting
> firmware-allocated buffers via identity mappings. One common use-
> case where this is required is if early firmware or bootloaders
> have set up a bootsplash framebuffer that a display controller is
> actively scanning out from during the operating system boot
> process.
>
> 2. If an "iommu-addresses" property exists without a "reg" property,
> the reserved-memory node describes an IOVA reservation. Such memory
> regions are excluded from the IOVA space available to operating
> system drivers and can be used for regions that must not be used to
> map arbitrary buffers.

Bah, I've only just realised: don't we also need to change the "oneOf:
required: ..." schema to permit "iommu-addresses" without "reg" or "size"?

Thanks,
Robin.

> Each mapping or reservation is tied to a specific device via a phandle
> to the device's device tree node. This allows a reserved-memory region
> to be reused across multiple devices.
>
> Reviewed-by: Rob Herring <robh@kernel.org>
> Reviewed-by: Robin Murphy <robin.murphy@arm.com>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
> Changes in v9:
> - add Reviewed-by tags
>
> Changes in v8:
> - include validation warnings that had crept into an unrelated patch
>
> Changes in v7:
> - keep reserved-memory.txt to avoid broken references
>
> Changes in v6:
> - add device phandle to iommu-addresses property in examples
> - remove now unused dt-bindings/reserved-memory.h header
>
> .../reserved-memory/reserved-memory.yaml | 70 +++++++++++++++++++
> 1 file changed, 70 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml
> index 44f72bcf1782..fb48d016e368 100644
> --- a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml
> +++ b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml
> @@ -52,6 +52,30 @@ properties:
> Address and Length pairs. Specifies regions of memory that are
> acceptable to allocate from.
>
> + iommu-addresses:
> + $ref: /schemas/types.yaml#/definitions/phandle-array
> + description: >
> + A list of phandle and specifier pairs that describe static IO virtual
> + address space mappings and carveouts associated with a given reserved
> + memory region. The phandle in the first cell refers to the device for
> + which the mapping or carveout is to be created.
> +
> + The specifier consists of an address/size pair and denotes the IO
> + virtual address range of the region for the given device. The exact
> + format depends on the values of the "#address-cells" and "#size-cells"
> + properties of the device referenced via the phandle.
> +
> + When used in combination with a "reg" property, an IOVA mapping is to
> + be established for this memory region. One example where this can be
> + useful is to create an identity mapping for physical memory that the
> + firmware has configured some hardware to access (such as a bootsplash
> + framebuffer).
> +
> + If no "reg" property is specified, the "iommu-addresses" property
> + defines carveout regions in the IOVA space for the given device. This
> + can be useful if a certain memory region should not be mapped through
> + the IOMMU.
> +
> no-map:
> type: boolean
> description: >
> @@ -97,4 +121,50 @@ oneOf:
>
> additionalProperties: true
>
> +examples:
> + - |
> + / {
> + compatible = "foo";
> + model = "foo";
> +
> + #address-cells = <2>;
> + #size-cells = <2>;
> +
> + reserved-memory {
> + #address-cells = <2>;
> + #size-cells = <2>;
> + ranges;
> +
> + adsp_resv: reservation-adsp {
> + /*
> + * Restrict IOVA mappings for ADSP buffers to the 512 MiB region
> + * from 0x40000000 - 0x5fffffff. Anything outside is reserved by
> + * the ADSP for I/O memory and private memory allocations.
> + */
> + iommu-addresses = <&adsp 0x0 0x00000000 0x00 0x40000000>,
> + <&adsp 0x0 0x60000000 0xff 0xa0000000>;
> + };
> +
> + fb: framebuffer@90000000 {
> + reg = <0x0 0x90000000 0x0 0x00800000>;
> + iommu-addresses = <&dc0 0x0 0x90000000 0x0 0x00800000>;
> + };
> + };
> +
> + bus@0 {
> + #address-cells = <1>;
> + #size-cells = <1>;
> + ranges = <0x0 0x0 0x0 0x40000000>;
> +
> + adsp: adsp@2990000 {
> + reg = <0x2990000 0x2000>;
> + memory-region = <&adsp_resv>;
> + };
> +
> + dc0: display@15200000 {
> + reg = <0x15200000 0x10000>;
> + memory-region = <&fb>;
> + };
> + };
> + };
> ...