lk2nd: device: Add an LED driver

Signed-off-by: Yang Xiwen <[email protected]>

Author: 185264646

Documentation/dt-bindings.md

@@ -247,3 +247,34 @@ new keycode to the actual key.
 		};
 	};
 ```
+
+### GPIO leds
+
+lk2nd supports the `gpio-leds` node. This node follows upstream binding except
+that most properties are not supported. Currently only `gpios` and
+`default-state` are supported in lk2nd.
+
+```
+gpio-leds {
+    compatible = "gpio-leds";
+
+    red {
+        gpios = <&tlmm 3 GPIO_ACTIVE_HIGH>;
+        default-state = "on";
+    };
+
+    green {
+        gpios = <&tlmm 4 GPIO_ACTIVE_HIGH>;
+        default-state = "off";
+    };
+};
+```
+
+This driver is mainly for lk1st since no previous boot-loader is capable to
+light up an LED in this case. This makes it unclear what state currently the
+device is in. If you wish to make sure some leds are enabled or disabled by
+lk1st on boot, you can use this driver.
+
+lk2nd doesn't implement a fully-fledged led subsystem. The only purpose for
+this driver is for debugging and the LED behavior consistancy between lk1st
+and lk2nd.

lk2nd/device/leds.c

@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/* Copyright (c) 2025 Yang Xiwen <[email protected]> */
+
+#include <debug.h>
+#include <libfdt.h>
+
+#include <lk2nd/hw/gpio.h>
+
+#include "device.h"
+
+static int lk2nd_leds_init(const void *dtb, int node)
+{
+	int i = 0, subnode, len;
+	struct gpiol_desc desc;
+	const char *state;
+
+	dprintf(SPEW, " Initializing LEDs\n");
+	dprintf(SPEW, " | label | gpio        | state |\n");
+
+	fdt_for_each_subnode(subnode, dtb, node) {
+		state = fdt_getprop(dtb, subnode, "default-state", &len);
+		if (len < 0 || state[len - 1] != '\0') {
+			dprintf(CRITICAL, "leds: Failed to get property \"default-state\". Broken dtb?\n");
+			continue;
+		}
+
+		if (!strcmp(state, "on")) {
+			gpiol_get(dtb, subnode, NULL, &desc, GPIOL_FLAGS_OUT_ASSERTED);
+		} else if (!strcmp(state, "off")) {
+			gpiol_get(dtb, subnode, NULL, &desc, GPIOL_FLAGS_OUT_DEASSERTED);
+		} else if (!strcmp(state, "keep")) {
+			/* do nothing */
+		} else {
+			dprintf(CRITICAL, "leds: Unknown \"default-state\" value: %s\n", state);
+			continue;
+		}
+
+		i++;
+
+		dprintf(SPEW, " | %5s | 0x%02x 0x%04x | %5s |\n",
+			fdt_get_name(dtb, subnode, NULL), desc.dev, desc.pin, state);
+	}
+	dprintf(INFO, "leds: %d leds configured\n", i);
+
+	if (subnode < 0 && subnode != -FDT_ERR_NOTFOUND) {
+		dprintf(CRITICAL, "leds: Failed to parse subnodes: %d\n", subnode);
+		return subnode;
+	}
+
+	return 0;
+}
+
+LK2ND_DEVICE_INIT("gpio-leds", lk2nd_leds_init);

lk2nd/device/rules.mk

@@ -18,6 +18,7 @@ OBJS += \
 	$(LK2ND_DEVICE_OBJ) \
 	$(LOCAL_DIR)/panel.o \
 	$(LOCAL_DIR)/keys.o \
+	$(LOCAL_DIR)/leds.o \
 
 ifneq ($(LK2ND_COMPATIBLE),)
 DEFINES += LK2ND_COMPATIBLE="$(LK2ND_COMPATIBLE)"