Re: [PATCH v5 2/5] dt-bindings: arm: fsl: add imx-se-fw binding doc

[Rob Herring <robh@kernel.org>]

On Fri, Jul 12, 2024 at 11:49:57AM +0530, Pankaj Gupta wrote:
> The NXP security hardware IP(s) like: i.MX EdgeLock Enclave, V2X etc.,
> creates an embedded secure enclave within the SoC boundary to enable
> features like:
> - HSM
> - SHE
> - V2X
> 
> Secure-Enclave(s) communication interface are typically via message
> unit, i.e., based on mailbox linux kernel driver. This driver enables
> communication ensuring well defined message sequence protocol between
> Application Core and enclave's firmware.
> 
> Driver configures multiple misc-device on the MU, for multiple
> user-space applications, to be able to communicate over single MU.
> 
> It exists on some i.MX processors. e.g. i.MX8ULP, i.MX93 etc.
> 
> Signed-off-by: Pankaj Gupta <pankaj.gupta@nxp.com>
> ---
>  .../devicetree/bindings/firmware/fsl,imx-se.yaml   | 111 +++++++++++++++++++++
>  1 file changed, 111 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/firmware/fsl,imx-se.yaml b/Documentation/devicetree/bindings/firmware/fsl,imx-se.yaml
> new file mode 100644
> index 000000000000..bd99505de6e6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/firmware/fsl,imx-se.yaml
> @@ -0,0 +1,111 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/firmware/fsl,imx-se.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: NXP i.MX HW Secure Enclave(s) EdgeLock Enclave
> +
> +maintainers:
> +  - Pankaj Gupta <pankaj.gupta@nxp.com>
> +
> +description: |
> +  NXP's SoC may contain one or multiple embedded secure-enclave HW
> +  IP(s) like i.MX EdgeLock Enclave, V2X etc. These NXP's HW IP(s)
> +  enables features like
> +    - Hardware Security Module (HSM),
> +    - Security Hardware Extension (SHE), and
> +    - Vehicular to Anything (V2X)
> +
> +  Communication interface to the secure-enclaves is based on the
> +  messaging unit(s).
> +
> +properties:
> +  $nodename:
> +    pattern: "firmware@[0-9a-f]+$"
> +
> +  compatible:
> +    enum:
> +      - fsl,imx8ulp-se
> +      - fsl,imx93-se
> +      - fsl,imx95-se
> +
> +  reg:
> +    maxItems: 1
> +    description: Identifier of the communication interface to secure-enclave.

I don't understand what this is. How does someone determine what the 
value should be? Are there constraints on the values?

> +
> +  mboxes:
> +    items:
> +      - description: mailbox phandle to send message to se firmware

"mailbox phandle to " is redundant. Drop.

> +      - description: mailbox phandle to receive message from se firmware
> +
> +  mbox-names:
> +    description: two names are to be listed, one for rx and other one for tx.
> +      The name can be any of the below list.

I think this can be dropped. The schema says all this.

> +    items:
> +      - const: tx
> +      - const: rx
> +
> +  memory-region:
> +    items:
> +      - description: The phandle to the reserved external memory, the only
> +          accessible memoryregion to secure enclave(SE) firmware. It is an
> +          optional property based on compatible.
> +          (see bindings/reserved-memory/reserved-memory.txt)

Drop. 'maxItems: 1' is sufficient.

> +
> +  sram:
> +    items:
> +      - description: It is an optional property based on compatible.

Drop. 'maxItems: 1' is sufficient.

> +
> +required:
> +  - compatible
> +  - reg
> +  - mboxes
> +  - mbox-names
> +
> +allOf:
> +  # memory-region
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - fsl,imx8ulp-se
> +              - fsl,imx93-se
> +    then:
> +      required:
> +        - memory-region
> +    else:
> +      properties:
> +        memory-region: false
> +
> +  # sram
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - fsl,imx8ulp-se
> +    then:
> +      required:
> +        - sram
> +
> +    else:
> +      properties:
> +        sram: false
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    firmware {
> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      firmware@0 {
> +        compatible = "fsl,imx95-se";
> +        reg = <0x0>;
> +        mboxes = <&ele_mu0 0 0>, <&ele_mu0 1 0>;
> +        mbox-names = "tx", "rx";
> +      };
> +    };
> +...
> 
> -- 
> 2.34.1
>