Add documentation for a general GPIO cascade. It allows building one-to-many cascades of GPIO lines using multiplexer to choose the cascaded line. Signed-off-by: Mauri Sandberg <maukka@xxxxxxxxxxxx> Reviewed-by: Rob Herring <robh@xxxxxxxxxx> Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx> --- v7 -> v8: - added Reviewed-by tag by Linus v6 -> v7: - no changes v5 -> v6: - added Reviewed-by tag by Rob v4 -> v5: - renamed gpio-mux-input -> gpio-cascade - changed vague term 'pin' to 'upstream line' - added more verbose description for the module - added missing 'mux-controls' entry - dropped Tested-by and Reviewed-by due to changes in bindings v3 -> v4: - Changed author email - Included Tested-by and Reviewed-by from Drew v2 -> v3: added a complete example on dual 4-way multiplexer v1 -> v2: added a little bit more text in the binding documenation --- .../bindings/gpio/gpio-cascade.yaml | 103 ++++++++++++++++++ 1 file changed, 103 insertions(+) create mode 100644 Documentation/devicetree/bindings/gpio/gpio-cascade.yaml diff --git a/Documentation/devicetree/bindings/gpio/gpio-cascade.yaml b/Documentation/devicetree/bindings/gpio/gpio-cascade.yaml new file mode 100644 index 000000000000..46248f8e2ba5 --- /dev/null +++ b/Documentation/devicetree/bindings/gpio/gpio-cascade.yaml @@ -0,0 +1,103 @@ +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/gpio/gpio-cascade.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: Generic GPIO cascade + +maintainers: + - Mauri Sandberg <maukka@xxxxxxxxxxxx> + +description: | + A generic GPIO cascade + + This hardware construction cascades (multiplexes) several GPIO lines from + one-to-many using a software controlled multiplexer. The most common use + case is probably reading several inputs by switching the multiplexer over + several input lines, which in practice works well since input lines has + high impedance. + + Constructions with multiplexed outputs are also possible using open drain + electronics. + + The number of cascaded GPIO lines is limited by the technology used to + switch over the cascaded lines. There are readily available dual/triple + 4-to-1 multiplexers, for example, and others. + + Illustration (pins used to drive the multiplexer are omitted for clarity) + + /|---- Cascaded GPIO line 0 + Upstream | |---- Cascaded GPIO line 1 + GPIO line ----+ | . + | | . + \|---- Cascaded GPIO line n + +properties: + compatible: + enum: + - gpio-cascade + + gpio-controller: true + + '#gpio-cells': + const: 2 + + mux-controls: + minItems: 1 + maxItems: 1 + description: | + The mux controller that will be driving the GPIO cascade. + + upstream-gpios: + description: | + The GPIO line used as the upstream line will convey the status to/from + cascaded GPIO lines. In an input mode, by using this line, it is + possible to read the status from selected cascaded GPIO line. + + In an output mode the status of the upstream GPIO will be conveyed to + the selected cascaded GPIO line. + +required: + - compatible + - gpio-controller + - "#gpio-cells" + - mux-controls + - upstream-gpios + +additionalProperties: false + +examples: + - | + #include <dt-bindings/gpio/gpio.h> + mux: mux-controller { + compatible = "gpio-mux"; + #mux-control-cells = <0>; + + mux-gpios = <&gpio 9 GPIO_ACTIVE_HIGH>, + <&gpio 11 GPIO_ACTIVE_HIGH>; + }; + + gpio2: key-mux1 { + compatible = "gpio-cascade"; + mux-controls = <&mux>; + + gpio-controller; + #gpio-cells = <2>; + + // GPIOs used by this node, upstream pin + upstream-gpios = <&gpio 12 GPIO_ACTIVE_HIGH>; + }; + + gpio3: key-mux2 { + compatible = "gpio-cascade"; + mux-controls = <&mux>; + + gpio-controller; + #gpio-cells = <2>; + + // GPIOs used by this node, upstream pin + upstream-gpios = <&gpio 14 GPIO_ACTIVE_HIGH>; + }; + +... -- 2.25.1
