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 <chris.packham@xxxxxxxxxxxxxxxxxxx>
---
.../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 000000000000..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>;
+
+ spi-dev@0 {
+ compatible = "...";
+ reg = <0>;
+ }
+
+ spi-dev@1 {
+ compatible = "...";
+ reg = <1>;
+ }
+ };
--
2.21.0
