linux-kernel - Re: [PATCH v3 6/8] dt-bindings: microchip,sparx5-spi-mux: Add Sparx5 SPI mux driver bindings

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Date:   Mon, 13 Jul 2020 13:29:02 -0600
From:   Rob Herring <robh@...nel.org>
To:     Lars Povlsen <lars.povlsen@...rochip.com>
Cc:     Mark Brown <broonie@...nel.org>, Peter Rosin <peda@...ntia.se>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Serge Semin <fancer.lancer@...il.com>,
        Serge Semin <Sergey.Semin@...kalelectronics.ru>
Subject: Re: [PATCH v3 6/8] dt-bindings: microchip,sparx5-spi-mux: Add Sparx5
 SPI mux driver bindings

On Thu, Jul 02, 2020 at 12:13:29PM +0200, Lars Povlsen wrote:
> The Microchip Sparx5 SPI controller has two bus segments, and use this
> mux to control the bus interface mapping for any chip selects. This
> decribes the bindings used to configure the mux driver.
> 
> Signed-off-by: Lars Povlsen <lars.povlsen@...rochip.com>
> ---
>  .../mux/microchip,sparx5-spi-mux.yaml         | 71 +++++++++++++++++++
>  1 file changed, 71 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mux/microchip,sparx5-spi-mux.yaml
> 
> diff --git a/Documentation/devicetree/bindings/mux/microchip,sparx5-spi-mux.yaml b/Documentation/devicetree/bindings/mux/microchip,sparx5-spi-mux.yaml
> new file mode 100644
> index 0000000000000..b0ce3b15a69e5
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mux/microchip,sparx5-spi-mux.yaml
> @@ -0,0 +1,71 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/mux/microchip,sparx5-spi-mux.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Microchip Sparx5 SPI mux
> +
> +maintainers:
> +  - Lars Povlsen <lars.povlsen@...rochip.com>
> +
> +description: |
> +  The Microchip Sparx5 SPI controller has two bus segments. In order
> +  to switch between the appropriate bus for any given SPI slave
> +  (defined by a chip select), this mux driver is used. The device tree
> +  node for the mux will define the bus mapping for any chip
> +  selects. The default bus mapping for any chip select is "0", such
> +  that only non-default mappings need to be explicitly defined.
> +
> +properties:
> +  compatible:
> +    enum:
> +      - microchip,sparx5-spi-mux
> +
> +  '#address-cells':
> +    const: 1
> +
> +  '#size-cells':
> +    const: 0
> +
> +  '#mux-control-cells':
> +    const: 0
> +
> +required:
> +  - compatible
> +
> +additionalProperties: false
> +
> +patternProperties:
> +  "^mux@[0-9a-f]$":
> +    type: object
> +
> +    properties:
> +      reg:
> +        description:
> +          Chip select to define bus mapping for.
> +        minimum: 0
> +        maximum: 15
> +
> +      microchip,bus-interface:
> +        description:
> +          The bus interface to use for this chip select.
> +        $ref: /schemas/types.yaml#/definitions/uint32
> +        enum: [0, 1]
> +
> +    required:
> +      - reg
> +      - microchip,bus-interface
> +
> +examples:
> +  - |
> +    mux: mux-controller {
> +      compatible = "microchip,sparx5-spi-mux";
> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      #mux-control-cells = <0>;

How is this mux accessed? You have no control interface defined.

> +      mux@e {
> +        reg = <14>;
> +        microchip,bus-interface = <1>;

This looks odd. I take it that there's 2 muxes for this h/w? If so then 
#mux-control-cells should be 1 and the cell value can be whatever you 
want that is meaningful for the mux controller. Could be 0,1 or perhaps 
0xe if that's more useful.

Rob