dt-bindings: spi: Document binding for generic SPI multiplexer

# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)

%YAML 1.2

---

$id: http://devicetree.org/schemas/spi/spi-mux.yaml#

$schema: http://devicetree.org/meta-schemas/core.yaml#

title: Generic SPI Multiplexer

description: |

  This binding describes a SPI bus multiplexer to route the SPI chip select

  signals. This can be used when you need more devices than the SPI controller

  has chip selects available. An example setup is shown in ASCII art; the actual

  setting of the multiplexer to a channel needs to be done by a specific SPI mux

  driver.

        MOSI /--------------------------------+--------+--------+--------\

        MISO |/------------------------------+|-------+|-------+|-------\|

         SCL ||/----------------------------+||------+||------+||------\||

             |||                            |||      |||      |||      |||

      +------------+                        |||      |||      |||      |||

      | SoC  |||   |                      +-+++-+  +-+++-+  +-+++-+  +-+++-+

      |      |||   |                      | dev |  | dev |  | dev |  | dev |

      |   +--+++-+ | CS-X  +------+\      +--+--+  +--+--+  +--+--+  +--+--+

      |   | SPI  +-|-------+ Mux  |\\   CS-0 |        |        |        |

      |   +------+ |       +--+---+\\\-------/   CS-1 |        |        |

      |            |          |    \\\----------------/   CS-2 |        |

      |   +------+ |          |     \\-------------------------/   CS-3 |

      |   | ?    +-|----------/      \----------------------------------/

      |   +------+ |

      +------------+

allOf:

  - $ref: "/schemas/spi/spi-controller.yaml#"

maintainers:

  - Chris Packham <chris.packham@alliedtelesis.co.nz>

properties:

  compatible:

    const: spi-mux

  mux-controls:

    maxItems: 1

required:

   - compatible

   - reg

   - spi-max-frequency

   - mux-controls

examples:

   - |

     #include <dt-bindings/gpio/gpio.h>

     mux: mux-controller {

       compatible = "gpio-mux";

       #mux-control-cells = <0>;

       mux-gpios = <&gpio0 3 GPIO_ACTIVE_HIGH>;

     };

     spi {

       #address-cells = <1>;

       #size-cells = <0>;

       spi@0 {

         compatible = "spi-mux";

         reg = <0>;

         #address-cells = <1>;

         #size-cells = <0>;

         spi-max-frequency = <100000000>;

         mux-controls = <&mux>;

         spi-flash@0 {

           compatible = "jedec,spi-nor";

           reg = <0>;

           #address-cells = <1>;

           #size-cells = <0>;

           spi-max-frequency = <40000000>;

         };

         spi-device@1 {

           compatible = "lineartechnology,ltc2488";

           reg = <1>;

           #address-cells = <1>;

           #size-cells = <0>;

           spi-max-frequency = <10000000>;

         };

       };

     };