Re: [PATCH v3 2/5] dt-bindings: arm: fsl: add imx-se-fw binding doc

[Conor Dooley <conor@kernel.org>]

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On Mon, Jun 17, 2024 at 12:59:40PM +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   | 160 +++++++++++++++++++++
>  1 file changed, 160 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..60ad1c4a3dfa
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/firmware/fsl,imx-se.yaml
> @@ -0,0 +1,160 @@
> +# 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:
> +  $nodename:
> +    pattern: "^[0-9a-z]*-if@[0-9a-f]+$"

Just "firmware@<hex>" please.

> +
> +  compatible:
> +    enum:
> +      - fsl,imx8ulp-se
> +      - fsl,imx93-se
> +      - fsl,imx95-se
> +
> +  reg:
> +    maxItems: 1
> +    description: Identifier of the communication interface to secure-enclave.
> +
> +  mboxes:
> +    description: contain a list of phandles to mailboxes.
> +    items:
> +      - description: Specify the mailbox used to send message to se firmware
> +      - description: Specify the mailbox used to receive message from se firmware
> +
> +  mbox-names:
> +    items:
> +      - const: tx
> +      - const: rx
> +      - const: txdb
> +      - const: rxdb
> +    minItems: 2
> +
> +  memory-region:
> +    description: contains a list of phandles to reserved external memory.
> +    items:
> +      - description: It is used by secure-enclave firmware. It is an optional
> +          property based on compatible and identifier to communication interface.
> +          (see bindings/reserved-memory/reserved-memory.txt)
> +
> +  sram:
> +    description: contains a list of phandles to sram.

There's only 1 phandle allowed, don't describe it as a list.
Same for memory-region.

> +    $ref: /schemas/types.yaml#/definitions/phandle-array
> +    items:
> +      - description: Phandle to the device SRAM. It is an optional property
> +          based on compatible and identifier to communication interface.
> +
> +allOf:
> +  # memory-region
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - fsl,imx8ulp-se
> +              - fsl,imx93-se
> +    then:
> +      required:
> +        - memory-region

> +    else:
> +      not:
> +        required:
> +          - memory-region

Use

else: properties: memory-region: false

Same for sram. Sort the allOf after required.

> +
> +  # sram
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - fsl,imx8ulp-se
> +    then:
> +      required:
> +        - sram
> +    else:
> +      not:
> +        required:
> +          - sram
> +
> +required:
> +  - compatible
> +  - reg
> +  - mboxes
> +  - mbox-names
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    firmware {

You've made up these firmware "buses" here, what purpose do they serve,
other than allowing you to have a reg property?

> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      ele-if@0 {
> +        compatible = "fsl,imx8ulp-se";
> +        reg = <0x0>;

What does the reg property even do? Is it ever more than 0? Can this
information be provided as a mbox cell?

> +        mboxes = <&s4muap 0 0>, <&s4muap 1 0>;
> +        mbox-names = "tx", "rx";
> +        sram = <&sram0>;
> +        memory-region = <&ele_reserved>;
> +      };
> +    };
> +  - |
> +    firmware {

These examples are all basically the same, drop all but one.

Thanks,
Conor.

> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      ele-if@0 {
> +        compatible = "fsl,imx93-se";
> +        reg = <0x0>;
> +        mboxes = <&s4muap 0 0>, <&s4muap 1 0>;
> +        mbox-names = "tx", "rx";
> +        memory-region = <&ele_reserved>;
> +      };
> +    };
> +  - |
> +    firmware {
> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      ele-if@0 {
> +        compatible = "fsl,imx95-se";
> +        reg = <0x0>;
> +        mboxes = <&ele_mu0 0 0>, <&ele_mu0 1 0>;
> +        mbox-names = "tx", "rx";
> +      };
> +      v2x-if@3 {
> +        compatible = "fsl,imx95-se";
> +        reg = <0x3>;
> +        mboxes = <&v2x_mu 0 0>, <&v2x_mu 1 0>;
> +        mbox-names = "tx", "rx";
> +      };
> +      v2x-if@4 {
> +        compatible = "fsl,imx95-se";
> +        reg = <0x4>;
> +        mboxes = <&v2x_mu6 0 0>, <&v2x_mu6 1 0>;
> +        mbox-names = "tx", "rx";
> +      };
> +      v2x-if@5 {
> +        compatible = "fsl,imx95-se";
> +        reg = <0x5>;
> +        mboxes = <&v2x_mu7 0 0>, <&v2x_mu7 1 0>;
> +        mbox-names = "tx", "rx";
> +      };
> +    };
> +...
> 
> -- 
> 2.34.1
> 

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