Re: [PATCH 1/9] dt-bindings: Arm: Add Firmware Framework for Armv8-A (FF-A) binding

Jonathan Cameron
2020-09-01T16:07:00Z

On Sat, 29 Aug 2020 18:09:15 +0100
Sudeep Holla <sudeep.holla@arm.com> wrote:

> From: Will Deacon <will@kernel.org>
>
> Add devicetree bindings for a FF-A-compliant hypervisor, its partitions
> and their memory regions. The naming is ludicrous but also not by fault.
>
> Signed-off-by: Will Deacon <will@kernel.org>
> (sudeep.holla: Dropped PSA from name and elsewhere as it seem to have
> disappeared mysteriously just before the final release)
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

As I was reading this out of curiosity...

I'm far from a yaml expert but a few things in line.

> ---
> .../devicetree/bindings/arm/arm,ffa.yaml | 102 ++++++++++++++++++
> .../reserved-memory/arm,ffa-memory.yaml | 71 ++++++++++++
> 2 files changed, 173 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/arm/arm,ffa.yaml
> create mode 100644 Documentation/devicetree/bindings/reserved-memory/arm,ffa-memory.yaml
>
> diff --git a/Documentation/devicetree/bindings/arm/arm,ffa.yaml b/Documentation/devicetree/bindings/arm/arm,ffa.yaml
> new file mode 100644
> index 000000000000..668a5995fcab
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/arm,ffa.yaml
> @@ -0,0 +1,102 @@
> +# SPDX-License-Identifier: GPL-2.0
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/arm/arm,ffa.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Arm Firmware Framework for Arm v8-A
> +
> +maintainers:
> + - Will Deacon <will@kernel.org>
> +
> +description: |
> + Firmware frameworks implementing partition setup according to the FF-A
> + specification defined by ARM document number ARM DEN 0077A ("Arm Firmware
> + Framework for Arm v8-A") [0] must provide a "manifest and image" for each
> + partition to the "partition manager" so that the partition execution contexts
> + can be initialised.
> +
> + In the case of a virtual FFA instance, the manifest and image details can be
> + passed to the hypervisor (e.g. Linux KVM) using this binding.
> +
> + [0] https://developer.arm.com/docs/den0077/latest
> +
> +properties:
> + $nodename:
> + const: ffa_hyp
> +
> + compatible:
> + oneOf:
> + - const: arm,ffa-1.0-hypervisor

As below, would enum be more appropriate here?

> +
> + memory-region:
> + $ref: '/schemas/types.yaml#/definitions/phandle'
> + description: |
> + A phandle to the reserved memory region [1] to be used by the hypervisor.
> + The reserved memory region must be compatible with
> + "arm,ffa-1.0-hypervisor-memory-region".
> +
> + [1] Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> +
> +patternProperties:
> + "^ffa_partition[0-9]+$":
> + type: object
> + description: One or more child nodes, each describing an FFA partition.
> + properties:
> + $nodename:
> + const: ffa_partition
> +
> + compatible:
> + oneOf:
enum?
> + - const: arm,ffa-1.0-partition
> +
> + uuid:
> + $ref: '/schemas/types.yaml#definitions/string'
> + description: |
> + The 128-bit UUID [2] of the service implemented by this partition.
> +
> + [2] https://tools.ietf.org/html/rfc4122

Feels like we should be able to better type wise than a string for this but
maybe not... Doesn't seem to be much in the way of precedence.

> +
> + nr-exec-ctxs:
> + $ref: '/schemas/types.yaml#/definitions/uint32'
> + description: |
> + The number of virtual CPUs to instantiate for this partition.
> +
> + exec-state:
> + description: The execution state in which to execute the partition.
> + oneOf:
> + - const: "AArch64"
> + - const: "AArch32"
> +
> + entry-point:
> + $ref: '/schemas/types.yaml#/definitions/uint32-matrix'
> + description: |
> + The entry address of the partition specified as an Intermediate
> + Physical Address (IPA) encoded according to the '#address-cells'
> + property.
> +
> + memory-region:
> + $ref: '/schemas/types.yaml#/definitions/phandle-array'
> + description: |
> + A list of phandles to FFA reserved memory regions [3] for this
> + partition.
> +
> + [3] Documentation/devicetree/bindings/reserved-memory/arm,ffa-memory.yaml
> +
> +additionalProperties: false
> +
> +examples:
> + - |
> + ffa_hyp {
> + compatible = "arm,ffa-1.0-hypervisor";
> + memory-region = <&ffa_hyp_reserved>;
> +
> + ffa_partition0 {
> + compatible = "arm,ffa-1.0-partition";
> + uuid = "12345678-9abc-def0-1234-56789abcdef0";
> + nr-exec-ctxs = <2>;
> + exec-state = "AArch64";
> + entry-point = <0x80000>;
> + memory-region = <&ffa_reserved0 &ffa_reserved1>;
> + };
> + };
> diff --git a/Documentation/devicetree/bindings/reserved-memory/arm,ffa-memory.yaml b/Documentation/devicetree/bindings/reserved-memory/arm,ffa-memory.yaml
> new file mode 100644
> index 000000000000..5335e07abcfc
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/reserved-memory/arm,ffa-memory.yaml
> @@ -0,0 +1,71 @@
> +# SPDX-License-Identifier: GPL-2.0
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/reserved-memory/arm,ffa-memory.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Memory Region for Arm Firmware Framework for Arm v8-A
> +
> +maintainers:
> + - Will Deacon <will@kernel.org>
> +
> +description: |
> + This binding allows a FF-A implementation to describe the normal memory
> + regions of a partition [1] to a hypervisor according to [2].
> +
> + The physical address range reserved for the partition can be specified as a
> + static allocation using the 'reg' property or as a dynamic allocation using
> + the 'size' property. If both properties are omitted, then the hypervisor can
> + allocate physical memory for the partition however it sees fit.
> +
> + [1] Documentation/devicetree/bindings/arm/arm,ffa.yaml
> + [2] Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> +
> +properties:
> + $nodename:
> + pattern: "^ffa_mem(@[0-9a-f]+)?$"
> +
> + compatible:
> + oneOf:
> + - const: arm,ffa-1.0-partition-memory-region

If there is just element and it is const why not just?
compatible:
const: ....

I guess it sort of future proofs you for later variants...
However in that case, it would be more common to use

compatible:
enum:
- arm,ffa...

which is more restrictive but doesn't seem like you need the complexity of
oneOf and it's handling of sub schemas here.

> +
> + ipa-range:
> + $ref: '/schemas/types.yaml#/definitions/uint32-matrix'
> + description: |
> + The Intermediate Physical Address (IPA) range (encoded in the same way as
> + a 'reg' property) at which to map the physical memory. If the IPA range is
> + larger than the physical memory region then the region is mapped starting
> + at the base of the IPA range.
> +
> + read-only:
> + type: boolean
> + description: |
> + (static allocation only) The memory region has been pre-populated
> + by the firmware framework and must be mapped without write permission
> + at stage 2.
> +
> + non-executable:
> + type: boolean
> + description: |
> + The memory region must be mapped without execute permission at stage 2.
> +
> +
> +required:
> + - compatible
> +
> +# The "reserved-memory" binding defines additional properties.
> +additionalProperties: true
> +
> +examples:
> + - |
> + reserved-memory {
> + #address-cells = <2>;
> + #size-cells = <2>;
> +
> + ffa_reserved0: ffa_mem@100000000 {
> + compatible = "arm,ffa-1.0-partition-memory-region";
> + reg = <0x1 0x0 0x0 0x04000000>; // 64M @ 1GB

Isn't that at 4GB?

> + ipa-range = <0x0 0x0 0x0 0x04000000>; // 64M @ 0x0
> + read-only;
> + };
> + };