Re: [PATCH 2/3] dt-bindings: firmware: add mbedtee,rpc binding

[Krzysztof Kozlowski <krzk@kernel.org>]

On 01/07/2026 15:25, Xing Loong wrote:
> Add YAML devicetree binding for the MbedTEE Trusted Execution

Drop YAML, there is no such thing as YAML binding.

> Environment driver.

We don't take bindings for drivers but for hardware or firmware. Please
describe these instead.

> 
> The binding covers two platform configurations:
>   - ARM/AArch64 (TrustZone, SMC): two reserved-memory regions
>     (rpc-t2r-ring and rpc-t2r-shm) plus a GIC SPI edge interrupt
>     for TEE-to-REE notifications.
>   - RISC-V (IMSIC): three reserved-memory regions, adding
>     rpc-r2t-ring for REE-to-TEE command submissions; no interrupts
>     property (T2R notifications use IMSIC MSI allocated at runtime).
> 
> Signed-off-by: Xing Loong <xing.xl.loong@gmail.com>
> ---
>  .../bindings/firmware/mbedtee,rpc.yaml        | 221 ++++++++++++++++++
>  1 file changed, 221 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/firmware/mbedtee,rpc.yaml
> 
> diff --git a/Documentation/devicetree/bindings/firmware/mbedtee,rpc.yaml b/Documentation/devicetree/bindings/firmware/mbedtee,rpc.yaml
> new file mode 100644
> index 0000000..08ae255
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/firmware/mbedtee,rpc.yaml
> @@ -0,0 +1,221 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/firmware/mbedtee,rpc.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: MbedTEE Trusted Execution Environment
> +
> +maintainers:
> +  - Xing Loong <xing.xl.loong@gmail.com>
> +
> +description: |
> +  MbedTEE is a Trusted Execution Environment for embedded systems.
> +  This binding describes the shared-memory regions used for RPC

Describe firmware, not the binding. It's redundant to say what the
binding is about, just say what is the hardware.

> +  communication between the Linux REE driver and MbedTEE OS.
> +
> +  The REE and TEE CPUs sharing the RPC memory must be in a
> +  hardware-coherent domain (same CPU cluster, coherent caches).
> +
> +  Two or three reserved-memory regions are required:
> +
> +    rpc-t2r-ring  ring buffer for TEE-to-REE notifications (all platforms)
> +    rpc-t2r-shm   shared memory for TEE-to-REE RPC payloads (all platforms)
> +    rpc-r2t-ring  ring buffer for REE-to-TEE command submissions (RISC-V only)
> +
> +  On ARM/AArch64 the transport uses SMC calls; TEE-to-REE
> +  notifications use a GIC SPI edge interrupt.
> +
> +  On RISC-V the TEE notifies the REE via IMSIC MSI; the REE submits
> +  commands via shared-memory rpc-r2t-ring that the TEE polls. No
> +  REE-to-TEE interrupt is used. No SBI ecall is involved.
> +
> +properties:
> +  $nodename:
> +    const: mbedtee

Drop, why would it be relevant?

> +
> +  compatible:
> +    const: mbedtee,rpc

Feels way too generic. First, Google results on mbedtee are basically
non-existing, so what sort of company is that?

Second, rpc is just not specific enough. Please carefully read writing
bindings doc.

> +
> +  interrupts:
> +    description:
> +      GIC interrupt used by the TEE to notify the REE of pending RPC
> +      responses (ARM/AArch64 only). Not present on RISC-V platforms which
> +      use IMSIC platform MSI interrupts allocated dynamically at runtime.

Please read writing bindings doc.

> +
> +  msi-parent:
> +    maxItems: 1
> +    description:
> +      IMSIC MSI controller used by the Linux driver to allocate the

Again drivers...

> +      TEE-to-REE notification interrupt on RISC-V platforms. Not present on
> +      ARM/AArch64 platforms, which use the interrupts property.
> +
> +  memory-region:
> +    minItems: 2
> +    maxItems: 3
> +    description:
> +      References to reserved-memory regions for REE<->TEE communication.
> +      Entries must match memory-region-names order.

Obvious. Please do not come with your own style of bindings.

> +
> +  memory-region-names:
> +    minItems: 2
> +    maxItems: 3

Why is this flexible?

> +    items:
> +      enum:
> +        - rpc-t2r-ring

rpc is redundant, drop

> +        - rpc-t2r-shm
> +        - rpc-r2t-ring
> +
> +required:
> +  - compatible
> +
> +allOf:
> +  - if:
> +      required:
> +        - interrupts
> +    then:
> +      required:
> +        - interrupts
> +        - memory-region
> +        - memory-region-names
> +      properties:
> +        msi-parent: false
> +        memory-region:
> +          minItems: 2
> +          maxItems: 2
> +        memory-region-names:
> +          items:
> +            - const: rpc-t2r-ring
> +            - const: rpc-t2r-shm
> +    else:
> +      required:
> +        - msi-parent
> +        - memory-region
> +        - memory-region-names

So memory-region is always required?

> +      properties:
> +        memory-region:
> +          minItems: 3
> +          maxItems: 3
> +        memory-region-names:
> +          items:
> +            - const: rpc-t2r-ring
> +            - const: rpc-t2r-shm
> +            - const: rpc-r2t-ring

Your top level schema said that. You only need minItems.

> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    /* ARM TrustZone (SMC) */
> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
> +    / {
> +      #address-cells = <2>;
> +      #size-cells = <2>;
> +
> +      gic: interrupt-controller@2f000000 {
> +        compatible = "arm,gic-v3";
> +        reg = <0 0x2f000000 0 0x10000>,
> +              <0 0x2f100000 0 0x200000>;
> +        interrupt-controller;
> +        #interrupt-cells = <3>;
> +      };
> +
> +      reserved-memory {
> +        #address-cells = <2>;
> +        #size-cells = <2>;
> +        ranges;
> +
> +        mbedtee_t2r_ring: rpc-t2r-ring@85f10000 {
> +          reg = <0 0x85f10000 0 0x20000>;
> +          no-map;
> +        };
> +
> +        mbedtee_t2r_shm: rpc-t2r-shm@85f30000 {
> +          reg = <0 0x85f30000 0 0x40000>;
> +          no-map;
> +        };
> +      };

None of the above is relevant, drop.


> +
> +      firmware {
> +        mbedtee {
> +          compatible = "mbedtee,rpc";
> +          interrupt-parent = <&gic>;
> +          interrupts = <GIC_SPI 72 IRQ_TYPE_EDGE_RISING>;
> +          memory-region = <&mbedtee_t2r_ring>, <&mbedtee_t2r_shm>;
> +          memory-region-names = "rpc-t2r-ring", "rpc-t2r-shm";
> +        };
> +      };
> +    };
> +


Best regards,
Krzysztof