dt-bindings: gpio: Add gpio-latch binding document

This adds a binding for a GPIO multiplexer driver based on latches
connected to other GPIOs.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/devicetree/bindings/gpio/gpio-latch.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/gpio/gpio-latch.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: GPIO latch controller
+
+maintainers:
+  - Sascha Hauer <s.hauer@pengutronix.de>
+
+description: |
+  This binding describes a GPIO multiplexer based on latches connected to
+  other GPIOs, like this:
+
+  CLK0 ----------------------.        ,--------.
+  CLK1 -------------------.  `--------|>    #0 |
+                          |           |        |
+  OUT0 ----------------+--|-----------|D0    Q0|-----|<
+  OUT1 --------------+-|--|-----------|D1    Q1|-----|<
+  OUT2 ------------+-|-|--|-----------|D2    Q2|-----|<
+  OUT3 ----------+-|-|-|--|-----------|D3    Q3|-----|<
+  OUT4 --------+-|-|-|-|--|-----------|D4    Q4|-----|<
+  OUT5 ------+-|-|-|-|-|--|-----------|D5    Q5|-----|<
+  OUT6 ----+-|-|-|-|-|-|--|-----------|D6    Q6|-----|<
+  OUT7 --+-|-|-|-|-|-|-|--|-----------|D7    Q7|-----|<
+         | | | | | | | |  |           `--------'
+         | | | | | | | |  |
+         | | | | | | | |  |           ,--------.
+         | | | | | | | |  `-----------|>    #1 |
+         | | | | | | | |              |        |
+         | | | | | | | `--------------|D0    Q0|-----|<
+         | | | | | | `----------------|D1    Q1|-----|<
+         | | | | | `------------------|D2    Q2|-----|<
+         | | | | `--------------------|D3    Q3|-----|<
+         | | | `----------------------|D4    Q4|-----|<
+         | | `------------------------|D5    Q5|-----|<
+         | `--------------------------|D6    Q6|-----|<
+         `----------------------------|D7    Q7|-----|<
+                                      `--------'
+
+  The number of clk-gpios and latched-gpios is not fixed. The actual number
+  of number of latches and the number of inputs per latch is derived from
+  the number of GPIOs given in the corresponding device tree properties.
+
+properties:
+  compatible:
+    const: gpio-latch
+  "#gpio-cells":
+    const: 2
+
+  clk-gpios:
+    description: Array of GPIOs to be used to clock a latch
+
+  latched-gpios:
+    description: Array of GPIOs to be used as inputs per latch
+
+  setup-duration-ns:
+    description: Delay in nanoseconds to wait after the latch inputs have been
+      set up
+
+  clock-duration-ns:
+    description: Delay in nanoseconds to wait between clock output changes
+
+  gpio-controller: true
+
+  gpio-line-names: true
+
+required:
+  - compatible
+  - "#gpio-cells"
+  - gpio-controller
+  - clk-gpios
+  - latched-gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    gpio-latch {
+        #gpio-cells = <2>;
+        pinctrl-names = "default";
+        pinctrl-0 = <&pinctrl_di_do_leds>;
+        compatible = "gpio-latch";
+        gpio-controller;
+        setup-duration-ns = <100>;
+        clock-duration-ns = <100>;
+
+        clk-gpios = <&gpio3 7 0>, <&gpio3 8 0>;
+        latched-gpios = <&gpio3 21 0>, <&gpio3 22 0>,
+                       <&gpio3 23 0>, <&gpio3 24 0>,
+                       <&gpio3 25 0>, <&gpio3 26 0>,
+                       <&gpio3 27 0>, <&gpio3 28 0>;
+    };