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

Add binding documentation for the spi-mux driver. This allows a generic
multiplexer to be used to provide access to multiple SPI devices.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200204032838.20739-2-chris.packham@alliedtelesis.co.nz
Signed-off-by: Mark Brown <broonie@kernel.org>
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Chris Packham 2020-02-04 16:28:37 +13:00 committed by Mark Brown
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Documentation/devicetree/bindings/spi/spi-mux.yaml Normal file
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# 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>;
};
};
};