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 <[email protected]>
---
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 <[email protected]>
+
+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
On Mon, 21 Jun 2021 20:20:52 +0300, Mauri Sandberg wrote:
> 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 <[email protected]>
> ---
> 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
>
Reviewed-by: Rob Herring <[email protected]>