drivers: leds: leds-multi: control several LEDs synchronously

A multi LED may control up to 9 single LED by different
brightness values.
Each decimal place represents one single LED:

  0 = off
  1-8 =  max_brightness * n / 8
  9 = max_brightness

The timer trigger may toggle the LED-array while
the brightness value of the multi-led defines,
which LEDs of the array toggle with which brightness.

The "pattern" trigger may be used to switch the colors
for a specific time to blink any pattern in multiple colors.

This allows an easy implementation of multicolor LEDs,
without API extension or breaks.

Signed-off-by: Christian Hohnstaedt <Christian.Hohnstaedt@wago.com>

drivers/leds/Kconfig

@@ -892,6 +892,20 @@ config LEDS_ACER_A500
 	  This option enables support for the Power Button LED of
 	  Acer Iconia Tab A500.
 
+config LEDS_MULTI
+	tristate "Control multiple LEDs by one trigger"
+	depends on LEDS_CLASS
+	help
+	  This is a virtual LED, controlling up to 9 simple LEDs.
+	  Each LED is controlled by a decimal digit of the brightness
+	  of this virtual LED. It may for example control the 3 single LEDs of
+	  an RGB multi-color LED. The timer trigger turns them on and off
+	  while the brightness value controls the color.
+	  Together with the pattern trigger, even "enterprisey"
+	  error codes blinked to users, running lights and other things
+	  are possible without complex user-space code.
+	  If unsure say N.
+
 source "drivers/leds/blink/Kconfig"
 
 comment "Flash and Torch LED drivers"

drivers/leds/Makefile

@@ -88,6 +88,7 @@ obj-$(CONFIG_LEDS_TURRIS_OMNIA)		+= leds-turris-omnia.o
 obj-$(CONFIG_LEDS_WM831X_STATUS)	+= leds-wm831x-status.o
 obj-$(CONFIG_LEDS_WM8350)		+= leds-wm8350.o
 obj-$(CONFIG_LEDS_WRAP)			+= leds-wrap.o
+obj-$(CONFIG_LEDS_MULTI)		+= leds-multi.o
 
 # LED SPI Drivers
 obj-$(CONFIG_LEDS_CR0014114)		+= leds-cr0014114.o

drivers/leds/leds-multi.c

@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Driver for orchestrating several LEDs
+ *
+ * Copyright (C) 2020 Christian Hohnstaedt <christian.hohnstaedt@wago.com>
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/ctype.h>
+#include <linux/of.h>
+
+#include "leds.h"
+
+#define DRVNAME "multi-led"
+#define MAX_LEDS 9
+
+struct multi_led {
+	struct led_classdev cdev;
+	int num_leds;
+	struct led_classdev *leds[MAX_LEDS];
+};
+
+static void multi_led_set(struct led_classdev *led_cdev,
+			  enum led_brightness value)
+{
+	struct multi_led *mled = container_of(led_cdev, struct multi_led, cdev);
+	int i, v;
+
+	for (i = 0, v = value; i < mled->num_leds; i++, v /= 10) {
+		int val = mled->leds[i]->max_brightness;
+
+		switch (v % 10) {
+		case 0:
+			val = 0;
+			break;
+		case 9:
+			break;
+		default:
+			if (val >= 8)
+				val = val * (v % 10) / 8;
+			break;
+		}
+		led_set_brightness(mled->leds[i], val);
+	}
+}
+
+static struct led_classdev *find_child_led(phandle phandle)
+{
+	struct led_classdev *led;
+	struct device_node *node = of_find_node_by_phandle(phandle);
+	const char *label;
+	int len;
+
+	len = strlen(label);
+	down_read(&leds_list_lock);
+	list_for_each_entry(led, &leds_list, node) {
+		if (node == led->dev->of_node) {
+			up_read(&leds_list_lock);
+			return led;
+		}
+	}
+	up_read(&leds_list_lock);
+	return NULL;
+}
+
+static int multi_led_probe(struct platform_device *pdev)
+{
+	int size, i;
+	struct multi_led *mled;
+	const __be32 *list;
+	struct device_node *np = pdev->dev.of_node;
+	struct property *prop;
+
+	mled = devm_kzalloc(&pdev->dev, sizeof(*mled), GFP_KERNEL);
+	if (!mled)
+		return -ENOMEM;
+
+	prop = of_find_property(np, "leds", &size);
+	mled->num_leds = size / sizeof(*list);
+	if (mled->num_leds > MAX_LEDS)
+		return -EINVAL;
+
+	list = prop->value;
+	mled->cdev.max_brightness = 1;
+	mled->cdev.brightness_set = multi_led_set;
+
+	for (i = 0; i < mled->num_leds; i++) {
+		mled->leds[i] = find_child_led(be32_to_cpup(list++));
+		mled->cdev.max_brightness *= 10;
+		if (mled->leds[i] == NULL)
+			return -EPROBE_DEFER;
+		led_trigger_remove(mled->leds[i]);
+	}
+	mled->cdev.max_brightness--;
+	if (of_property_read_string(np, "label", &mled->cdev.name))
+		return -EINVAL;
+
+	return devm_led_classdev_register(&pdev->dev, &mled->cdev);
+}
+
+static const struct of_device_id multi_led_of_match[] = {
+	{ .compatible = "multi_led", },
+	{ /* sentinel */ },
+};
+MODULE_DEVICE_TABLE(of, multi_led_of_match);
+
+static struct platform_driver multi_led_driver = {
+	.probe = multi_led_probe,
+	.driver	= {
+		.name = DRVNAME,
+		.of_match_table = of_match_ptr(multi_led_of_match),
+	},
+};
+
+static int __init multi_led_init(void)
+{
+	return platform_driver_register(&multi_led_driver);
+}
+
+static void __exit multi_led_exit(void)
+{
+	platform_driver_unregister(&multi_led_driver);
+}
+
+module_init(multi_led_init);
+module_exit(multi_led_exit);
+
+MODULE_AUTHOR("Christian Hohnstaedt <christian.hohnstaedt@wago.com>");
+MODULE_DESCRIPTION("Multi LED driver");
+MODULE_LICENSE("GPL");
+