leds: class: Store the color index in struct led_classdev

Store the color of the LED so that it is not lost after the LED's
name has been composed. This color information can then be exposed to
the user space or used by the LED consumer.

Signed-off-by: Jean-Jacques Hiblot <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

Documentation/ABI/testing/sysfs-class-led

···
 		brightness. Reading this file when no hw brightness change
 		event has happened will return an ENODATA error.
 
+What:		/sys/class/leds/<led>/color
+Date:		June 2023
+KernelVersion:	6.5
+Description:
+		Color of the LED.
+
+		This is a read-only file. Reading this file returns the color
+		of the LED as a string (e.g: "red", "green", "multicolor").
+
 What:		/sys/class/leds/<led>/trigger
 Date:		March 2006
 KernelVersion:	2.6.17

drivers/leds/led-class.c

···
 }
 static DEVICE_ATTR_RO(max_brightness);
 
+static ssize_t color_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	const char *color_text = "invalid";
+	struct led_classdev *led_cdev = dev_get_drvdata(dev);
+
+	if (led_cdev->color < LED_COLOR_ID_MAX)
+		color_text = led_colors[led_cdev->color];
+
+	return sysfs_emit(buf, "%s\n", color_text);
+}
+static DEVICE_ATTR_RO(color);
+
 #ifdef CONFIG_LEDS_TRIGGERS
 static BIN_ATTR(trigger, 0644, led_trigger_read, led_trigger_write, 0);
 static struct bin_attribute *led_trigger_bin_attrs[] = {
···
 static struct attribute *led_class_attrs[] = {
 	&dev_attr_brightness.attr,
 	&dev_attr_max_brightness.attr,
+	&dev_attr_color.attr,
 	NULL,
 };
 
···
 			fwnode_property_read_u32(init_data->fwnode,
 				"max-brightness",
 				&led_cdev->max_brightness);
+
+			if (fwnode_property_present(init_data->fwnode, "color"))
+				fwnode_property_read_u32(init_data->fwnode, "color",
+							 &led_cdev->color);
 		}
 	} else {
 		proposed_name = led_cdev->name;
···
 	ret = led_classdev_next_name(proposed_name, final_name, sizeof(final_name));
 	if (ret < 0)
 		return ret;
+
+	if (led_cdev->color >= LED_COLOR_ID_MAX)
+		dev_warn(parent, "LED %s color identifier out of range\n", final_name);
 
 	mutex_init(&led_cdev->led_access);
 	mutex_lock(&led_cdev->led_access);

include/linux/leds.h

···
 	const char		*name;
 	unsigned int brightness;
 	unsigned int max_brightness;
+	unsigned int color;
 	int			 flags;
 
 	/* Lower 16 bits reflect status */