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>

diff --git a/drivers/leds/rgb/Kconfig b/drivers/leds/rgb/Kconfig
index 360c867..183bccc 100644 (file)
--- a/drivers/leds/rgb/Kconfig
+++ b/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

diff --git a/drivers/leds/rgb/Makefile b/drivers/leds/rgb/Makefile
index 8c01daf..c11cc56 100644 (file)
--- a/drivers/leds/rgb/Makefile
+++ b/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

diff --git a/drivers/leds/rgb/leds-group-multicolor.c b/drivers/leds/rgb/leds-group-multicolor.c
new file mode 100644 (file)
index 0000000..39f58be
--- /dev/null
+++ b/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");