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

Thierry Reding
2022-05-18T13:01:46Z

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On Sun, May 15, 2022 at 12:45:54PM +0200, Janne Grunau wrote:
> 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.

Ugh... I evidently messed this one up. It's not ever close to what I had
in my device trees for testing. I'll make sure to fix those up properly
and also that they pass validation.

> > + };
> > +
> > + 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.

Good catch. I'll drop this file from the patch set. It's no longer
needed.

Thanks,
Thierry

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