use johannes4linux approach

.gitignore

@@ -14,6 +14,6 @@ driver/*.mod.c
 driver/*.mod.o
 driver/*.o
 driver/modules.order
-dtoverlay/*.dtbo
+driver/*.dtbo
 
 

driver/Makefile

@@ -1,11 +1,30 @@
-obj-m += counter.o
+NAME = counter
+obj-m += $(NAME).o
 
-KDIR := /lib/modules/$(shell uname -r)/build
+all: $(NAME).ko $(NAME).dtbo
-PWD  := $(shell pwd)
+	echo Builded Device Tree Overlay and kernel module
 
-all:
+$(NAME).ko:
-	$(MAKE) -C $(KDIR) M=$(PWD) modules
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
+
+$(NAME).dtbo: $(NAME).dts
+	dtc -@ -I dts -O dtb -o $@ $<
 
 clean:
-	$(MAKE) -C $(KDIR) M=$(PWD) clean
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
+	rm -rf $(NAME).dtbo
 	
+load:
+	sudo dtoverlay -d . $(NAME).dtbo
+	@echo "Overlay loaded"
+	sudo insmod ./$(NAME).ko
+	@echo "LKM loaded"
+
+unload:
+	sudo rmmod ./$(NAME).ko
+	@echo "LKM unloaded"
+	sudo dtoverlay -R $(NAME)
+	@echo "Overlay unloaded"
+
+list: 
+	sudo dtoverlay -l

driver/counter.c

@@ -1,59 +1,147 @@
-#include <linux/init.h>
 #include <linux/module.h>
-#include <linux/gpio/consumer.h>
+#include <linux/init.h>
-#include <linux/delay.h>
+#include <linux/mod_devicetable.h>
+#include <linux/property.h>
 #include <linux/platform_device.h>
+#include <linux/of_device.h>
+#include <linux/gpio/consumer.h>
+#include <linux/proc_fs.h>
 
-MODULE_LICENSE("GPL v2");
+/* Meta Information */
-MODULE_AUTHOR("Du");
+MODULE_LICENSE("GPL");
-MODULE_DESCRIPTION("GPIO consumer API example for two LEDs");
+MODULE_AUTHOR("Johannes 4 GNU/Linux");
+MODULE_DESCRIPTION("A simple LKM to parse the device tree for a specific device and its properties");
 
-static struct gpio_desc *led_blue;
+/* Declate the probe and remove functions */
-static struct gpio_desc *led_red;
+static int dt_probe(struct platform_device *pdev);
+static void dt_remove(struct platform_device *pdev);
 
-static int __init led_consumer_init(void)
+static struct of_device_id my_driver_ids[] = {
 	{
-    struct device *dev = NULL;
+		.compatible = "brightlight,mydev",
+	}, { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, my_driver_ids);
 
-    pr_info("GPIO consumer LED module loading\n");
+static struct platform_driver my_driver = {
+	.probe = dt_probe,
+	.remove = dt_remove,
+	.driver = {
+		.name = "my_device_driver",
+		.of_match_table = my_driver_ids,
+	},
+};
 
-    // GPIOs per Name aus dem Device Tree holen (via label oder node property)
+/* GPIO variable */
-    led_blue = gpiod_get(dev, "led-blue", GPIOD_OUT_LOW);
+static struct gpio_desc *my_led = NULL;
-    if (IS_ERR(led_blue)) {
+
-        pr_err("Failed to get GPIO for blue LED\n");
+static struct proc_dir_entry *proc_file;
-        return PTR_ERR(led_blue);
+
+/**
+ * @brief Write data to buffer
+ */
+static ssize_t my_write(struct file *File, const char *user_buffer, size_t count, loff_t *offs) {
+	switch (user_buffer[0]) {
+		case '0':
+		case '1':
+			gpiod_set_value(my_led, user_buffer[0] - '0');
+		default:
+			break;
+	}
+	return count;
 }
 
-    led_red = gpiod_get(dev, "led-red", GPIOD_OUT_LOW);
+static struct proc_ops fops = {
-    if (IS_ERR(led_red)) {
+	.proc_write = my_write,
-        pr_err("Failed to get GPIO for red LED\n");
+};
-        gpiod_put(led_blue);
+
-        return PTR_ERR(led_red);
+/**
+ * @brief This function is called on loading the driver 
+ */
+static int dt_probe(struct platform_device *pdev) {
+	struct device *dev = &pdev->dev;
+	const char *label;
+	int my_value, ret;
+
+	printk("dt_gpio - Now I am in the probe function!\n");
+
+	/* Check for device properties */
+	if(!device_property_present(dev, "label")) {
+		printk("dt_gpio - Error! Device property 'label' not found!\n");
+		return -1;
+	}
+	if(!device_property_present(dev, "my_value")) {
+		printk("dt_gpio - Error! Device property 'my_value' not found!\n");
+		return -1;
+	}
+	if(!device_property_present(dev, "green-led-gpio")) {
+		printk("dt_gpio - Error! Device property 'green-led-gpio' not found!\n");
+		return -1;
 	}
 
-    // Test: LEDs einschalten
+	/* Read device properties */
-    gpiod_set_value(led_blue, 1);
+	ret = device_property_read_string(dev, "label", &label);
-    gpiod_set_value(led_red, 1);
+	if(ret) {
-    msleep(500);
+		printk("dt_gpio - Error! Could not read 'label'\n");
-    gpiod_set_value(led_blue, 0);
+		return -1;
-    gpiod_set_value(led_red, 0);
+	}
+	printk("dt_gpio - label: %s\n", label);
+	ret = device_property_read_u32(dev, "my_value", &my_value);
+	if(ret) {
+		printk("dt_gpio - Error! Could not read 'my_value'\n");
+		return -1;
+	}
+	printk("dt_gpio - my_value: %d\n", my_value);
+
+	/* Init GPIO */
+	my_led = gpiod_get(dev, "green-led", GPIOD_OUT_LOW);
+	if(IS_ERR(my_led)) {
+		printk("dt_gpio - Error! Could not setup the GPIO\n");
+		return -1 * IS_ERR(my_led);
+	}
+
+	/* Creating procfs file */
+	proc_file = proc_create("my-led", 0666, NULL, &fops);
+	if(proc_file == NULL) {
+		printk("procfs_test - Error creating /proc/my-led\n");
+		gpiod_put(my_led);
+		return -ENOMEM;
+	}
 
-    pr_info("LEDs blinked using gpio/consumer\n");
 
 	return 0;
 }
 
-static void __exit led_consumer_exit(void)
+/**
-{
+ * @brief This function is called on unloading the driver 
-    gpiod_set_value(led_blue, 0);
+ */
-    gpiod_set_value(led_red, 0);
+static void dt_remove(struct platform_device *pdev) {
-
+	printk("dt_gpio - Now I am in the remove function\n");
-    gpiod_put(led_blue);
+	gpiod_put(my_led);
-    gpiod_put(led_red);
+	proc_remove(proc_file);
-
-    pr_info("GPIO consumer LED module unloaded\n");
 }
 
-module_init(led_consumer_init);
+/**
-module_exit(led_consumer_exit);
+ * @brief This function is called, when the module is loaded into the kernel
+ */
+static int __init my_init(void) {
+	printk("dt_gpio - Loading the driver...\n");
+	if(platform_driver_register(&my_driver)) {
+		printk("dt_gpio - Error! Could not load driver\n");
+		return -1;
+	}
+	return 0;
+}
+
+/**
+ * @brief This function is called, when the module is removed from the kernel
+ */
+static void __exit my_exit(void) {
+	printk("dt_gpio - Unload driver");
+	platform_driver_unregister(&my_driver);
+}
+
+module_init(my_init);
+module_exit(my_exit);
+
 

driver/counter.dts

@@ -0,0 +1,17 @@
+/dts-v1/;
+/plugin/;
+/ {
+  compatible = "brcm,bcm2835";
+  fragment@0 {
+    target-path = "/";
+    __overlay__ {
+      my_device {
+        compatible = "brightlight,mydev";
+        status = "okay";
+        label = "Test";
+        my_value = <12>;
+        green-led-gpio = <&gpio 21 0>; 
+      };
+    };
+  };
+};

dtoverlay/Makefile

@@ -1,29 +0,0 @@
-# Source and target file names
-DTS = counter.dts
-DTBO = counter.dtbo
-
-# Installation paths
-OVERLAY_DIR = /boot/overlays
-CONFIG_TXT = /boot/firmware/config.txt
-OVERLAY_NAME = counter
-
-all: $(DTBO)
-
-$(DTBO): $(DTS)
-	dtc -@ -I dts -O dtb -o $@ $<
-
-load: $(DTBO)
-	sudo dtoverlay -d . $(OVERLAY_NAME)
-	@echo "Overlay loaded"
-
-unload: $(DTBO)
-	sudo dtoverlay -R $(OVERLAY_NAME)
-	@echo "Overlay unloaded"
-
-list: 
-	sudo dtoverlay -l
-
-
-clean:
-	rm -f *.dtbo
-

dtoverlay/counter.dts

@@ -1,46 +0,0 @@
-/dts-v1/;
-/plugin/;
-
-/ {
-    compatible = "brcm,bcm2835";
-
-    fragment@0 {
-        target = <&gpio>;
-        __overlay__ {
-            gpio_led_blue: gpio_led_blues@26 {
-                brcm,pins = <26>;
-                brcm,function = <1>; // output
-                brcm,pull = <0>;     // no pull
-            };
-            gpio_led_red: gpio_led_reds@21 {
-                brcm,pins = <21>;
-                brcm,function = <1>; // output
-                brcm,pull = <0>;     // no pull
-            };
-        };
-    };
-
-    fragment@1 {
-        target-path = "/";
-        __overlay__ {
-            mygpioleds {
-                compatible = "my,gpio-led-controller";
-                pinctrl-names = "default";
-                pinctrl-0 = <&gpio_led_blue &gpio_led_red>;
-
-                led-blue {
-                    gpios = <&gpio 26 0>;
-                    label = "led-blue";
-                };
-
-                led-red {
-                    gpios = <&gpio 21 0>;
-                    label = "led-red";
-                };
-            };
-        };
-    };
-
-};
-
-