samples: drivers: add test sample for the PWM LED driver

This sample allows to test the led-pwm driver. The first "pwm-leds"
compatible device instance found in DT is used. For each LEDs attached
to this device (child nodes) the same test pattern (described below) is
executed. The LED API functions are used to control the LEDs.

Test pattern:

For each PWM LEDs (one after the other):

- turn on
- turn off
- increase the brightness gradually up to the maximum level
- blink (0.1 sec on, 0.1 sec off)
- blink (1 sec on, 1 sec off)
- turn off

Signed-off-by: Simon Guinot <simon.guinot@seagate.com>

samples/drivers/led_pwm/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.13.1)
+
+find_package(Zephyr HINTS $ENV{ZEPHYR_BASE})
+project(led_pwm)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})

samples/drivers/led_pwm/README.rst

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+.. _led_pwm:
+
+LED PWM sample application
+##########################
+
+Overview
+********
+
+This sample allows to test the led-pwm driver. The first "pwm-leds" compatible
+device instance found in DT is used. For each LEDs attached to this device
+(child nodes) the same test pattern (described below) is executed. The LED API
+functions are used to control the LEDs.
+
+Test pattern
+============
+
+For each PWM LEDs (one after the other):
+
+- turn on
+- turn off
+- increase the brightness gradually up to the maximum level
+- blink (0.1 sec on, 0.1 sec off)
+- blink (1 sec on, 1 sec off)
+- turn off
+
+Building and Running
+********************
+
+This sample can be built and executed on all the boards with PWM LEDs connected.
+The LEDs must be correctly described in the DTS: the compatible property of the
+device node must match "pwm-leds". And for each LED, a child node must be
+defined and the PWM configuration must be provided through a "pwms" phandle's
+node.

samples/drivers/led_pwm/prj.conf

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+CONFIG_LOG=y
+
+CONFIG_PWM=y
+
+CONFIG_LED=y
+CONFIG_LED_PWM=y

samples/drivers/led_pwm/sample.yaml

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+sample:
+  description: Demonstration of the PWM LED driver
+  name: PWM LED sample
+tests:
+  sample.drivers.led.led_pwm:
+    filter: dt_compat_enabled("pwm-leds")
+    tags: LED
+    depends_on: pwm

samples/drivers/led_pwm/src/main.c

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+/*
+ * Copyright (c) 2020 Seagate Technology LLC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <device.h>
+#include <errno.h>
+#include <drivers/led.h>
+#include <sys/util.h>
+#include <zephyr.h>
+
+#include <logging/log.h>
+LOG_MODULE_REGISTER(main, CONFIG_LOG_DEFAULT_LEVEL);
+
+#if DT_NODE_HAS_STATUS(DT_INST(0, pwm_leds), okay)
+#define LED_PWM_NODE_ID		DT_INST(0, pwm_leds)
+#define LED_PWM_DEV_NAME	DT_INST_PROP_OR(0, label, "LED_PWM_0")
+#else
+#error "No LED PWM device found"
+#endif
+
+#define LED_PWM_LABEL(led_node_id) DT_PROP_OR(led_node_id, label, NULL),
+
+const char *led_label[] = {
+	DT_FOREACH_CHILD(LED_PWM_NODE_ID, LED_PWM_LABEL)
+};
+
+const int num_leds = ARRAY_SIZE(led_label);
+
+#define MAX_BRIGHTNESS	100
+
+#define FADE_DELAY_MS	10
+#define FADE_DELAY	K_MSEC(FADE_DELAY_MS)
+
+/**
+ * @brief Run tests on a single LED using the LED API syscalls.
+ *
+ * @param led_pwm LED PWM device.
+ * @param led Number of the LED to test.
+ */
+static void run_led_test(const struct device *led_pwm, uint8_t led)
+{
+	int err;
+	uint16_t level;
+
+	LOG_INF("Testing LED %d (%s)", led, led_label[led] ? : "no label");
+
+	/* Turn LED on. */
+	err = led_on(led_pwm, led);
+	LOG_INF("  Turning on");
+	if (err < 0) {
+		LOG_ERR("err=%d", err);
+		return;
+	}
+	k_sleep(K_MSEC(1000));
+
+	/* Turn LED off. */
+	err = led_off(led_pwm, led);
+	LOG_INF("  Turning off");
+	if (err < 0) {
+		LOG_ERR("err=%d", err);
+		return;
+	}
+	k_sleep(K_MSEC(1000));
+
+	/* Increase LED brightness gradually up to the maximum level. */
+	LOG_INF("  Increasing brightness gradually");
+	for (level = 0; level <= MAX_BRIGHTNESS; level++) {
+		err = led_set_brightness(led_pwm, led, level);
+		if (err < 0) {
+			LOG_ERR("err=%d brightness=%d\n", err, level);
+			return;
+		}
+		k_sleep(FADE_DELAY);
+	}
+	k_sleep(K_MSEC(1000));
+
+	/* Set LED blinking (on: 0.1 sec, off: 0.1 sec) */
+	LOG_INF("  Blinking (on: 0.1 sec, off: 0.1 sec)");
+	err = led_blink(led_pwm, led, 100, 100);
+	if (err < 0) {
+		LOG_ERR("err=%d", err);
+		return;
+	}
+	k_sleep(K_MSEC(5000));
+
+	/* Enable LED blinking (on: 1 sec, off: 1 sec) */
+	LOG_INF("  Blinking (on: 1 sec, off: 1 sec)");
+	err = led_blink(led_pwm, led, 1000, 1000);
+	if (err < 0) {
+		LOG_ERR("err=%d", err);
+		return;
+	}
+	k_sleep(K_MSEC(5000));
+
+	/* Turn LED off. */
+	LOG_INF("  Turning off");
+	err = led_off(led_pwm, led);
+	if (err < 0) {
+		LOG_ERR("err=%d", err);
+		return;
+	}
+}
+
+void main(void)
+{
+	const struct device *led_pwm;
+	uint8_t led;
+
+	led_pwm = device_get_binding(LED_PWM_DEV_NAME);
+	if (led_pwm) {
+		LOG_INF("Found device %s", LED_PWM_DEV_NAME);
+	} else {
+		LOG_ERR("Device %s not found", LED_PWM_DEV_NAME);
+		return;
+	}
+
+	if (!num_leds) {
+		LOG_ERR("No LEDs found for %s", LED_PWM_DEV_NAME);
+		return;
+	}
+
+	do {
+		for (led = 0; led < num_leds; led++) {
+			run_led_test(led_pwm, led);
+		}
+	} while (true);
+}