On Fri, Apr 12, 2019 at 05:02:11PM +1200, Chris Packham wrote:
> Add binding documentation for spi-mux-gpio which is a slightly more
> complicated hardware implementation of using gpios to steer SPI chip
> selects.
>
> Signed-off-by: Chris Packham
> ---
> .../devicetree/bindings/spi/spi-mux-gpio.txt | 45 +++
> 1 file changed, 45 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/spi/spi-mux-gpio.txt
>
> diff --git a/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt
> b/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt
> new file mode 100644
> index ..a32f25321d37
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt
> @@ -0,0 +1,45 @@
> +SPI bus gpio multiplexer
> +
> +The SPI bus gpio multiplexer can be used to implement more complicated access
> +logic than can be supported with the cs-gpios property of a SPI bus.
> +
> +In the example below we have a SoC with a single SPI CS that is gated by the
> +state of a gpio to select the desired SPI device.
> +
> + +--+ CS+-+ CS0 ++
> + | || |--||
> + | || \ / | ++
> + | SoC|| + |
> + | | GPIO | / \ | CS1 ++
> + | || |--||
> + +--++-+ ++
> +
> +Required properties:
> +- compatible - must be "spi-mux-gpio"
> +- gpios - gpios used to implement the multiplexing logic
> +- spi-parent-bus - parent spi bus to use
> +
> +Optional properties:
> +- spi-parent-cs - chip select on parent bus to use. Defaults to 0 if not
> + specified.
> +
> +Example for a multiplexer with a single gpio:
> +
> + spi-mux {
> + compatible = "spi-mux-gpio";
> + #address-cells = <1>;
> + #size-cells = <0>;
> + gpios = <&gpio0 1 0>;
> + spi-parent-bus = <&spi0>;
> + spi-parent-cs = <0>;
Why is this out of band? We can do something similar to I2C and use the
mux-control binding:
spi {
mux@0 {
compatible = "spi-mux";
reg "0";
mux-controls = ...;
spi-dev@0 {};
spi-dev@1 {};
};
spi-dev@1 {};
};
Rob
