Re: [PATCH v5 1/5] dt-bindings: reserved-memory: Document iommu-addresses

Janne Grunau
2022-05-15T10:46:12Z

On 2022-05-12 21:00:48 +0200, 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.
>
> 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.
>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
> .../reserved-memory/reserved-memory.txt | 1 -
> .../reserved-memory/reserved-memory.yaml | 62 +++++++++++++++++++
> include/dt-bindings/reserved-memory.h | 8 +++
> 3 files changed, 70 insertions(+), 1 deletion(-)
> delete mode 100644 Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> create mode 100644 include/dt-bindings/reserved-memory.h
>
> diff --git a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> deleted file mode 100644
> index 1810701a8509..000000000000
> --- a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> +++ /dev/null
> @@ -1 +0,0 @@
> -This file has been moved to reserved-memory.yaml.
> diff --git a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml
> index 7a0744052ff6..3a769aa66e1c 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 +121,42 @@ oneOf:
>
> additionalProperties: true
>
> +examples:
> + - |
> + reserved-memory {
> + #address-cells = <2>;
> + #size-cells = <2>;
> + ranges;
> +
> + adsp: 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 = <0x0 0x00000000 0x00 0x40000000>,
> + <0x0 0x60000000 0xff 0xa0000000>;

This misses the device's phandle. One could argue it's not necessary for
reservations but it will complicate the parsing code and the current
parsing code is not prepared for it.

> + };
> +
> + fb: framebuffer@90000000 {
> + reg = <0x0 0x90000000 0x0 0x00800000>;
> + iommu-addresses = <&dc0 0x0 0x90000000 0x0 0x00800000>;
> + };
> + };
> +
> + bus@0 {
> + #address-cells = <2>;
> + #size-cells = <2>;
> +
> + adsp@2990000 {
> + reg = <0x0 0x2990000 0x0 0x2000>;
> + memory-region = <&adsp>;
> + };
> +
> + display@15200000 {
> + reg = <0x0 0x15200000 0x0 0x10000>;
> + memory-region = <&fb>;
> + };
> + };
> +
> ...
> diff --git a/include/dt-bindings/reserved-memory.h b/include/dt-bindings/reserved-memory.h
> new file mode 100644
> index 000000000000..174ca3448342
> --- /dev/null
> +++ b/include/dt-bindings/reserved-memory.h
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: (GPL-2.0+ or MIT) */
> +
> +#ifndef _DT_BINDINGS_RESERVED_MEMORY_H
> +#define _DT_BINDINGS_RESERVED_MEMORY_H
> +
> +#define MEMORY_REGION_IDENTITY_MAPPING 0x1
> +
> +#endif

This appears to be an unused leftover from a previous version.

Janne