Re: [RFC PATCH v3] dt-bindings: net: New binding mctp-i2c-controller

[Rob Herring <robh@kernel.org>]

On Thu, Sep 09, 2021 at 10:32:15AM +0800, Matt Johnston wrote:
> Used to define a local endpoint to communicate with MCTP peripherals
> attached to an I2C bus. This I2C endpoint can communicate with remote
> MCTP devices on the I2C bus.
> 
> In the example I2C topology below (matching the second yaml example) we
> have MCTP devices on busses i2c1 and i2c6. MCTP-supporting busses are
> indicated by the 'mctp-controller' DT property on an I2C bus node.
> 
> A mctp-i2c-controller I2C client DT node is placed at the top of the
> mux topology, since only the root I2C adapter will support I2C slave
> functionality.
>                                                .-------.
>                                                |eeprom |
>     .------------.     .------.               /'-------'
>     | adapter    |     | mux  --@0,i2c5------'
>     | i2c1       ----.*|      --@1,i2c6--.--.
>     |............|    \'------'           \  \  .........
>     | mctp-i2c-  |     \                   \  \ .mctpB  .
>     | controller |      \                   \  '.0x30   .
>     |            |       \  .........        \  '.......'
>     | 0x50       |        \ .mctpA  .         \ .........
>     '------------'         '.0x1d   .          '.mctpC  .
>                             '.......'          '.0x31   .
>                                                 '.......'
> (mctpX boxes above are remote MCTP devices not included in the DT at
> present, they can be hotplugged/probed at runtime. A DT binding for
> specific fixed MCTP devices could be added later if required)
> 
> Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
> 
> ---
> 
> Compared to v2 this patch changes the MCTP indicator to being a property
> on the I2C bus node.
> (Previous patches went only to DT list, I've now CCed linux-i2c)
> 
> Wolfram does this look OK to you?
> 
> Thanks,
> Matt
> ---
>  Documentation/devicetree/bindings/i2c/i2c.txt |  4 +
>  .../devicetree/bindings/net/mctp-i2c.yaml     | 94 +++++++++++++++++++
>  2 files changed, 98 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/net/mctp-i2c.yaml
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> index b864916e087f..fc3dd7ec0445 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> @@ -95,6 +95,10 @@ wants to support one of the below features, it should adapt these bindings.
>  - smbus-alert
>  	states that the optional SMBus-Alert feature apply to this bus.
>  
> +- mctp-controller
> +	indicates that the system is accessible via this bus as an endpoint for
> +	MCTP over I2C transport.
> +
>  Required properties (per child device)
>  --------------------------------------
>  
> diff --git a/Documentation/devicetree/bindings/net/mctp-i2c.yaml b/Documentation/devicetree/bindings/net/mctp-i2c.yaml
> new file mode 100644
> index 000000000000..d0ff7fa9e114
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/net/mctp-i2c.yaml
> @@ -0,0 +1,94 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/net/mctp-i2c.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: MCTP I2C transport binding
> +
> +maintainers:
> +  - Matt Johnston <matt@codeconstruct.com.au>
> +
> +description:

Needs '|' to maintain paragraphs.

> +  An mctp-i2c-controller defines a local MCTP endpoint on an I2C
> +  controller. MCTP I2C is specified by DMTF DSP0237.
> +
> +  An mctp-i2c-controller must be attached to an I2C adapter
> +  which supports slave functionality. I2C busses (either directly or as
> +  subordinate mux busses) are attached to the mctp-i2c-controller with
> +  a 'mctp-controller' property on each used bus. Each mctp-controller I2C bus
> +  will be presented to the host system as a separate MCTP I2C instance.

Odd line breaks here.

> +
> +properties:
> +  compatible:
> +    const: mctp-i2c-controller
> +
> +  reg:
> +    # 1<<30
> +    minimum: 1073741824

You can use hex: 0x40000000

> +    # 1<<30 | 0x7f
> +    maximum: 1073741951
> +    description:
> +      7 bit I2C address of the local endpoint.
> +      I2C_OWN_SLAVE_ADDRESS (1<<30) flag must be set.
> +
> +additionalProperties: false
> +
> +required:
> +  - compatible
> +  - reg
> +
> +examples:
> +  - |
> +    // Basic case of a single I2C bus
> +    #include <dt-bindings/i2c/i2c.h>
> +
> +    i2c0: i2cbus0 {

i2c {

> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      mctp-controller;
> +
> +      mctp@30 {
> +        compatible = "mctp-i2c-controller";
> +        reg = <(0x30 | I2C_OWN_SLAVE_ADDRESS)>;
> +      };
> +    };
> +
> +  - |
> +    // Mux topology with multiple MCTP-handling busses under
> +    // a single mctp-i2c-controller.
> +    // i2c1 and i2c6 can have MCTP devices, i2c5 does not.
> +    #include <dt-bindings/i2c/i2c.h>
> +
> +    i2c1: i2cbus1 {

i2c {

> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      mctp-controller;
> +
> +      mctp@50 {
> +        compatible = "mctp-i2c-controller";
> +        reg = <(0x50 | I2C_OWN_SLAVE_ADDRESS)>;
> +      };
> +    };
> +
> +    i2cmux0 {

i2c-mux {

> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      i2c-parent = <&i2c1>;
> +
> +      i2c5: i2c@0 {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +        reg = <0>;
> +        eeprom@33 {
> +          reg = <0x33>;
> +        };
> +      };
> +
> +      i2c6: i2c@1 {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +        reg = <1>;
> +        mctp-controller;
> +      };
> +    };
> -- 
> 2.30.2
> 
>