tests: gpio_api_1pin: rpi_pico2: Support using external pulldowns

Extend gpio_api_1pin so that tests can require a test fixture to provide
an external pulldown resistor to the board under test. Use the new
test-gpio-external-pulldown device tree binding to define where that
GPIO is, and, finally, add a device tree overlay for the Raspberry Pi
Pico 2 board that defines where the pulldown provided by the fixture
will be.

Tested locally using `--fixture gpio_external_pull_down` when running
Twister on the command line, or by creating and using a Hardware Map
file, in combination with a modified Pico 2.

Signed-off-by: Andrew Featherstone <andrew.featherstone@gmail.com>

tests/drivers/gpio/gpio_api_1pin/boards/rpi_pico2_rp2350a_m33.overlay

@@ -0,0 +1,13 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright (c) 2024 Andrew Featherstone <andrew.featherstone@gmail.com>
+ */
+
+/ {
+	resources {
+		compatible = "test-gpio-external-pulldown";
+		/* Choice of pin on the header is arbitrary. */
+		gpios = <&pico_header 15 GPIO_ACTIVE_HIGH>;
+	};
+};

tests/drivers/gpio/gpio_api_1pin/dts/bindings/test-gpio-external-pulldown.yaml

@@ -0,0 +1,18 @@
+#
+# Copyright (c) 2024 Andrew Featherstone <andrew.featherstone@gmail.com>
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+description: |
+    This binding provides resources required to build and run the
+    tests/drivers/gpio/gpio_api_1pin test in Zephyr on certain hardware.
+
+compatible: "test-gpio-external-pulldown"
+
+properties:
+  gpios:
+    type: phandle-array
+    required: true
+    description: |
+      Identity of a GPIO that will be configured as both an output and input.

tests/drivers/gpio/gpio_api_1pin/src/test_gpio_api.h

@@ -11,10 +11,18 @@
 #include <zephyr/drivers/gpio.h>
 #include <zephyr/ztest.h>
 
-#if DT_NODE_HAS_PROP(DT_ALIAS(led0), gpios)
-#define TEST_NODE            DT_GPIO_CTLR(DT_ALIAS(led0), gpios)
-#define TEST_PIN             DT_GPIO_PIN(DT_ALIAS(led0), gpios)
-#define TEST_PIN_DTS_FLAGS   DT_GPIO_FLAGS(DT_ALIAS(led0), gpios)
+/* If possible, use a dedicated GPIO with an external pulldown resistor.
+ * Otherwise, fallback to repurposing led0 as a GPIO. The latter won't always
+ * work as expected when reconfigured as an input.
+ */
+#if DT_NODE_HAS_STATUS(DT_INST(0, test_gpio_external_pulldown), okay)
+#define TEST_NODE          DT_GPIO_CTLR(DT_INST(0, test_gpio_external_pulldown), gpios)
+#define TEST_PIN           DT_GPIO_PIN(DT_INST(0, test_gpio_external_pulldown), gpios)
+#define TEST_PIN_DTS_FLAGS DT_GPIO_FLAGS(DT_INST(0, test_gpio_external_pulldown), gpios)
+#elif DT_NODE_HAS_PROP(DT_ALIAS(led0), gpios)
+#define TEST_NODE          DT_GPIO_CTLR(DT_ALIAS(led0), gpios)
+#define TEST_PIN           DT_GPIO_PIN(DT_ALIAS(led0), gpios)
+#define TEST_PIN_DTS_FLAGS DT_GPIO_FLAGS(DT_ALIAS(led0), gpios)
 #else
 #error Unsupported board
 #endif

tests/drivers/gpio/gpio_api_1pin/testcase.yaml

@@ -1,16 +1,19 @@
+common:
+  tags:
+    - drivers
+    - gpio
+  depends_on: gpio
+  min_flash: 48
 tests:
   drivers.gpio.1pin:
-    tags:
-      - drivers
-      - gpio
-    depends_on: gpio
-    min_flash: 48
+    filter: >
+      dt_enabled_alias_with_parent_compat("led0", "gpio-leds")
+      and not dt_compat_enabled("test-gpio-external-pulldown")
     # Fix exclude when we can exclude just sim run
     platform_exclude:
       - mps2/an385
       - mps2/an521/cpu0
       - neorv32
-    filter: dt_enabled_alias_with_parent_compat("led0", "gpio-leds")
   drivers.gpio.1pin.aw9523b:
     tags:
       - drivers
@@ -27,3 +30,9 @@ tests:
             dt_compat_enabled("arduino-header-r3")
     extra_dtc_overlay_files:
       - "boards/aw9523b_on_arduino_header.overlay"
+  drivers.gpio.1pin.external_pull_down:
+    # For testing boards that require a test fixture that provides a pulldown
+    # resistor on the GPIO used for the test.
+    filter: dt_compat_enabled("test-gpio-external-pulldown")
+    harness_config:
+      fixture: gpio_external_pull_down