leds: rgb: Add a multicolor LED driver to group monochromatic LEDs

Grouping multiple monochrome LEDs into a multicolor LED device has a few
benefits over handling the group in user-space:
- The state of the LEDs relative to each other is consistent. In other
  words, if 2 threads competes to set the LED to green and red, the
  end-result cannot be black or yellow.
- The multicolor LED as a whole can be driven through the sysfs LED
  interface.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@traphandler.com>
Reviewed-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230728153731.3742339-5-jjhiblot@traphandler.com
Signed-off-by: Lee Jones <lee@kernel.org>

drivers/leds/rgb/Kconfig

@@ -2,6 +2,18 @@
 
 if LEDS_CLASS_MULTICOLOR
 
+config LEDS_GROUP_MULTICOLOR
+	tristate "LEDs group multi-color support"
+	depends on OF || COMPILE_TEST
+	help
+	  This option enables support for monochrome LEDs that are grouped
+	  into multicolor LEDs which is useful in the case where LEDs of
+	  different colors are physically grouped in a single multi-color LED
+	  and driven by a controller that doesn't have multi-color support.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called leds-group-multicolor.
+
 config LEDS_PWM_MULTICOLOR
 	tristate "PWM driven multi-color LED Support"
 	depends on PWM

drivers/leds/rgb/Makefile

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 
+obj-$(CONFIG_LEDS_GROUP_MULTICOLOR)	+= leds-group-multicolor.o
 obj-$(CONFIG_LEDS_PWM_MULTICOLOR)	+= leds-pwm-multicolor.o
 obj-$(CONFIG_LEDS_QCOM_LPG)		+= leds-qcom-lpg.o
 obj-$(CONFIG_LEDS_MT6370_RGB)		+= leds-mt6370-rgb.o

drivers/leds/rgb/leds-group-multicolor.c

@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Multi-color LED built with monochromatic LED devices
+ *
+ * This driver groups several monochromatic LED devices in a single multicolor LED device.
+ *
+ * Compared to handling this grouping in user-space, the benefits are:
+ * - The state of the monochromatic LED relative to each other is always consistent.
+ * - The sysfs interface of the LEDs can be used for the group as a whole.
+ *
+ * Copyright 2023 Jean-Jacques Hiblot <jjhiblot@traphandler.com>
+ */
+
+#include <linux/err.h>
+#include <linux/leds.h>
+#include <linux/led-class-multicolor.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+
+struct leds_multicolor {
+	struct led_classdev_mc mc_cdev;
+	struct led_classdev **monochromatics;
+};
+
+static int leds_gmc_set(struct led_classdev *cdev, enum led_brightness brightness)
+{
+	struct led_classdev_mc *mc_cdev = lcdev_to_mccdev(cdev);
+	struct leds_multicolor *priv = container_of(mc_cdev, struct leds_multicolor, mc_cdev);
+	const unsigned int group_max_brightness = mc_cdev->led_cdev.max_brightness;
+	int i;
+
+	for (i = 0; i < mc_cdev->num_colors; i++) {
+		struct led_classdev *mono = priv->monochromatics[i];
+		const unsigned int mono_max_brightness = mono->max_brightness;
+		unsigned int intensity = mc_cdev->subled_info[i].intensity;
+		int mono_brightness;
+
+		/*
+		 * Scale the brightness according to relative intensity of the
+		 * color AND the max brightness of the monochromatic LED.
+		 */
+		mono_brightness = DIV_ROUND_CLOSEST(brightness * intensity * mono_max_brightness,
+						    group_max_brightness * group_max_brightness);
+
+		led_set_brightness(mono, mono_brightness);
+	}
+
+	return 0;
+}
+
+static void restore_sysfs_write_access(void *data)
+{
+	struct led_classdev *led_cdev = data;
+
+	/* Restore the write acccess to the LED */
+	mutex_lock(&led_cdev->led_access);
+	led_sysfs_enable(led_cdev);
+	mutex_unlock(&led_cdev->led_access);
+}
+
+static int leds_gmc_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct led_init_data init_data = {};
+	struct led_classdev *cdev;
+	struct mc_subled *subled;
+	struct leds_multicolor *priv;
+	unsigned int max_brightness = 0;
+	int i, ret, count = 0;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	for (;;) {
+		struct led_classdev *led_cdev;
+
+		led_cdev = devm_of_led_get_optional(dev, count);
+		if (IS_ERR(led_cdev))
+			return dev_err_probe(dev, PTR_ERR(led_cdev), "Unable to get LED #%d",
+					     count);
+		if (!led_cdev)
+			break;
+
+		priv->monochromatics = devm_krealloc_array(dev, priv->monochromatics,
+					count + 1, sizeof(*priv->monochromatics),
+					GFP_KERNEL);
+		if (!priv->monochromatics)
+			return -ENOMEM;
+
+		priv->monochromatics[count] = led_cdev;
+
+		max_brightness = max(max_brightness, led_cdev->max_brightness);
+
+		count++;
+	}
+
+	subled = devm_kcalloc(dev, count, sizeof(*subled), GFP_KERNEL);
+	if (!subled)
+		return -ENOMEM;
+	priv->mc_cdev.subled_info = subled;
+
+	for (i = 0; i < count; i++) {
+		struct led_classdev *led_cdev = priv->monochromatics[i];
+
+		subled[i].color_index = led_cdev->color;
+
+		/* Configure the LED intensity to its maximum */
+		subled[i].intensity = max_brightness;
+	}
+
+	/* Initialise the multicolor's LED class device */
+	cdev = &priv->mc_cdev.led_cdev;
+	cdev->flags = LED_CORE_SUSPENDRESUME;
+	cdev->brightness_set_blocking = leds_gmc_set;
+	cdev->max_brightness = max_brightness;
+	cdev->color = LED_COLOR_ID_MULTI;
+	priv->mc_cdev.num_colors = count;
+
+	init_data.fwnode = dev_fwnode(dev);
+	ret = devm_led_classdev_multicolor_register_ext(dev, &priv->mc_cdev, &init_data);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to register multicolor LED for %s.\n",
+				     cdev->name);
+
+	ret = leds_gmc_set(cdev, cdev->brightness);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to set LED value for %s.", cdev->name);
+
+	for (i = 0; i < count; i++) {
+		struct led_classdev *led_cdev = priv->monochromatics[i];
+
+		/*
+		 * Make the individual LED sysfs interface read-only to prevent the user
+		 * to change the brightness of the individual LEDs of the group.
+		 */
+		mutex_lock(&led_cdev->led_access);
+		led_sysfs_disable(led_cdev);
+		mutex_unlock(&led_cdev->led_access);
+
+		/* Restore the write access to the LED sysfs when the group is destroyed */
+		devm_add_action_or_reset(dev, restore_sysfs_write_access, led_cdev);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id of_leds_group_multicolor_match[] = {
+	{ .compatible = "leds-group-multicolor" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, of_leds_group_multicolor_match);
+
+static struct platform_driver leds_group_multicolor_driver = {
+	.probe		= leds_gmc_probe,
+	.driver		= {
+		.name	= "leds_group_multicolor",
+		.of_match_table = of_leds_group_multicolor_match,
+	}
+};
+module_platform_driver(leds_group_multicolor_driver);
+
+MODULE_AUTHOR("Jean-Jacques Hiblot <jjhiblot@traphandler.com>");
+MODULE_DESCRIPTION("LEDs group multicolor driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:leds-group-multicolor");