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

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Message-ID: <87y2nmjx72.fsf@soft-dev15.microsemi.net>
Date:   Tue, 14 Jul 2020 10:52:01 +0200
From:   Lars Povlsen <lars.povlsen@...rochip.com>
To:     Rob Herring <robh@...nel.org>
CC:     Lars Povlsen <lars.povlsen@...rochip.com>,
        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


Rob Herring writes:

> 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,

The intended use was for the SPI driver to use mux_control_select(mux,
<cs>) and then have the mux driver translate the <cs> to the right bus
interface, according to its configuration. The SPI driver would have a
"mux-controls" property bound to this mux.

Anyway, I am getting pushed in the direction of using the "mux-mmio" and
"spi-mux" combo, so this driver and bindings are being dropped again.

I am currently awaiting the "rx-sample-delay-ns" issue to be clarified
such that I can refresh the series.

Thank you for your comments!

> Rob

-- 
Lars Povlsen,
Microchip