[v8,1/5] dt-bindings: reserved-memory: Document iommu-addresses

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>
---
Changes in v8:
- include validation warning fixes 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(+)

On Mon, Sep 05, 2022 at 07:08:29PM +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>
> ---
> Changes in v8:
> - include validation warning fixes 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(+)

Thanks for being persistent with this. It looks good to me.

Reviewed-by: Rob Herring <robh@kernel.org>

I really don't like new common bindings with only 1 user, so I hope the 
Asahi folks chime in here. Or really anyone else look at it.

Rob

On 2022-09-05 18:08, 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.

This seems sufficiently robust to me, just one possibly-relevant point 
which I'll get to in the following patch...

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
> Changes in v8:
> - include validation warning fixes 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>;
> +        };
> +      };
> +    };
>   ...

On 2022-09-08 17:32:47 -0500, Rob Herring wrote:
> On Mon, Sep 05, 2022 at 07:08:29PM +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>
> > ---
> > Changes in v8:
> > - include validation warning fixes 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(+)
> 
> Thanks for being persistent with this. It looks good to me.
> 
> Reviewed-by: Rob Herring <robh@kernel.org>
> 
> I really don't like new common bindings with only 1 user, so I hope the 
> Asahi folks chime in here. Or really anyone else look at it.

The Asahi WIP display controller/processor driver uses this binding with 
static non 1:1 mappings. The binding is sufficient for our needs our 
needs.

Janne