avionic design with actual uboot and tooling

submodule of avionic design uboot bootloader and with included tools to
get you started , read readme.md and readme-tk1-loader.md

u-boot/drivers/led/Kconfig

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+menu "LED Support"
+
+config LED
+	bool "Enable LED support"
+	depends on DM
+	help
+	  Many boards have LEDs which can be used to signal status or alerts.
+	  U-Boot provides a uclass API to implement this feature. LED drivers
+	  can provide access to board-specific LEDs. Use of the device tree
+	  for configuration is encouraged.
+
+config SPL_LED
+	bool "Enable LED support in SPL"
+	depends on SPL && SPL_DM
+	help
+	  The LED subsystem adds a small amount of overhead to the image.
+	  If this is acceptable and you have a need to use LEDs in SPL,
+	  enable this option. You will need to enable device tree in SPL
+	  for this to work.
+
+config LED_GPIO
+	bool "LED support for GPIO-connected LEDs"
+	depends on LED && DM_GPIO
+	help
+	  Enable support for LEDs which are connected to GPIO lines. These
+	  GPIOs may be on the SoC or some other device which provides GPIOs.
+	  The GPIO driver must used driver model. LEDs are configured using
+	  the device tree.
+
+config SPL_LED_GPIO
+	bool "LED support for GPIO-connected LEDs in SPL"
+        depends on SPL_LED && DM_GPIO
+	help
+	  This option is an SPL-variant of the LED_GPIO option.
+	  See the help of LED_GPIO for details.
+
+endmenu

u-boot/drivers/led/Makefile

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+#
+# Copyright (c) 2015 Google, Inc
+# Written by Simon Glass <sjg@chromium.org>
+#
+# SPDX-License-Identifier:	GPL-2.0+
+#
+
+obj-y += led-uclass.o
+obj-$(CONFIG_$(SPL_)LED_GPIO) += led_gpio.o

u-boot/drivers/led/led-uclass.c

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+/*
+ * Copyright (c) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <led.h>
+#include <dm/root.h>
+#include <dm/uclass-internal.h>
+
+int led_get_by_label(const char *label, struct udevice **devp)
+{
+	struct udevice *dev;
+	struct uclass *uc;
+	int ret;
+
+	ret = uclass_get(UCLASS_LED, &uc);
+	if (ret)
+		return ret;
+	uclass_foreach_dev(dev, uc) {
+		struct led_uclass_plat *uc_plat = dev_get_uclass_platdata(dev);
+
+		/* Ignore the top-level LED node */
+		if (uc_plat->label && !strcmp(label, uc_plat->label))
+			return uclass_get_device_tail(dev, 0, devp);
+	}
+
+	return -ENODEV;
+}
+
+int led_set_on(struct udevice *dev, int on)
+{
+	struct led_ops *ops = led_get_ops(dev);
+
+	if (!ops->set_on)
+		return -ENOSYS;
+
+	return ops->set_on(dev, on);
+}
+
+UCLASS_DRIVER(led) = {
+	.id		= UCLASS_LED,
+	.name		= "led",
+	.per_device_platdata_auto_alloc_size = sizeof(struct led_uclass_plat),
+};

u-boot/drivers/led/led_gpio.c

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+/*
+ * Copyright (c) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <led.h>
+#include <asm/gpio.h>
+#include <dm/lists.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+struct led_gpio_priv {
+	struct gpio_desc gpio;
+};
+
+static int gpio_led_set_on(struct udevice *dev, int on)
+{
+	struct led_gpio_priv *priv = dev_get_priv(dev);
+
+	if (!dm_gpio_is_valid(&priv->gpio))
+		return -EREMOTEIO;
+
+	return dm_gpio_set_value(&priv->gpio, on);
+}
+
+static int led_gpio_probe(struct udevice *dev)
+{
+	struct led_uclass_plat *uc_plat = dev_get_uclass_platdata(dev);
+	struct led_gpio_priv *priv = dev_get_priv(dev);
+
+	/* Ignore the top-level LED node */
+	if (!uc_plat->label)
+		return 0;
+	return gpio_request_by_name(dev, "gpios", 0, &priv->gpio, GPIOD_IS_OUT);
+}
+
+static int led_gpio_remove(struct udevice *dev)
+{
+	/*
+	 * The GPIO driver may have already been removed. We will need to
+	 * address this more generally.
+	 */
+#ifndef CONFIG_SANDBOX
+	struct led_gpio_priv *priv = dev_get_priv(dev);
+
+	if (dm_gpio_is_valid(&priv->gpio))
+		dm_gpio_free(dev, &priv->gpio);
+#endif
+
+	return 0;
+}
+
+static int led_gpio_bind(struct udevice *parent)
+{
+	const void *blob = gd->fdt_blob;
+	struct udevice *dev;
+	int node;
+	int ret;
+
+	for (node = fdt_first_subnode(blob, parent->of_offset);
+	     node > 0;
+	     node = fdt_next_subnode(blob, node)) {
+		struct led_uclass_plat *uc_plat;
+		const char *label;
+
+		label = fdt_getprop(blob, node, "label", NULL);
+		if (!label) {
+			debug("%s: node %s has no label\n", __func__,
+			      fdt_get_name(blob, node, NULL));
+			return -EINVAL;
+		}
+		ret = device_bind_driver_to_node(parent, "gpio_led",
+						 fdt_get_name(blob, node, NULL),
+						 node, &dev);
+		if (ret)
+			return ret;
+		uc_plat = dev_get_uclass_platdata(dev);
+		uc_plat->label = label;
+	}
+
+	return 0;
+}
+
+static const struct led_ops gpio_led_ops = {
+	.set_on		= gpio_led_set_on,
+};
+
+static const struct udevice_id led_gpio_ids[] = {
+	{ .compatible = "gpio-leds" },
+	{ }
+};
+
+U_BOOT_DRIVER(led_gpio) = {
+	.name	= "gpio_led",
+	.id	= UCLASS_LED,
+	.of_match = led_gpio_ids,
+	.ops	= &gpio_led_ops,
+	.priv_auto_alloc_size = sizeof(struct led_gpio_priv),
+	.bind	= led_gpio_bind,
+	.probe	= led_gpio_probe,
+	.remove	= led_gpio_remove,
+};