text: // SPDX-License-Identifier: GPL-2.0
  // Copyright (c) 2009,2018 Daniel Mack <daniel@zonque.org>
  
  #include <linux/kernel.h>
  #include <linux/platform_device.h>
  #include <linux/leds.h>
  #include <linux/delay.h>
  #include <linux/gpio/consumer.h>
  #include <linux/slab.h>
  #include <linux/module.h>
  #include <linux/of.h>
  
  #define LED_LT3593_NAME "lt3593"
  
  struct lt3593_led_data {
  	struct led_classdev cdev;
  	struct gpio_desc *gpiod;
  };
  
  static int lt3593_led_set(struct led_classdev *led_cdev,
  			   enum led_brightness value)
  {
  	struct lt3593_led_data *led_dat =
  		container_of(led_cdev, struct lt3593_led_data, cdev);
  	int pulses;
  
  	/*
  	 * The LT3593 resets its internal current level register to the maximum
  	 * level on the first falling edge on the control pin. Each following
  	 * falling edge decreases the current level by 625uA. Up to 32 pulses
  	 * can be sent, so the maximum power reduction is 20mA.
  	 * After a timeout of 128us, the value is taken from the register and
  	 * applied is to the output driver.
  	 */
  
  	if (value == 0) {
  		gpiod_set_value_cansleep(led_dat->gpiod, 0);
  		return 0;
  	}
  
  	pulses = 32 - (value * 32) / 255;
  
  	if (pulses == 0) {
  		gpiod_set_value_cansleep(led_dat->gpiod, 0);
  		mdelay(1);
  		gpiod_set_value_cansleep(led_dat->gpiod, 1);
  		return 0;
  	}
  
  	gpiod_set_value_cansleep(led_dat->gpiod, 1);
  
  	while (pulses--) {
  		gpiod_set_value_cansleep(led_dat->gpiod, 0);
  		udelay(1);
  		gpiod_set_value_cansleep(led_dat->gpiod, 1);
  		udelay(1);
  	}
  
  	return 0;
  }
  
  static int lt3593_led_probe(struct platform_device *pdev)
  {
  	struct device *dev = &pdev->dev;
  	struct lt3593_led_data *led_data;
  	struct fwnode_handle *child;
  	int ret, state = LEDS_GPIO_DEFSTATE_OFF;
  	struct led_init_data init_data = {};
  	const char *tmp;
  
  	if (!dev->of_node)
  		return -ENODEV;
  
  	led_data = devm_kzalloc(dev, sizeof(*led_data), GFP_KERNEL);
  	if (!led_data)
  		return -ENOMEM;
  
  	if (device_get_child_node_count(dev) != 1) {
  		dev_err(dev, "Device must have exactly one LED sub-node.");
  		return -EINVAL;
  	}
  
  	led_data->gpiod = devm_gpiod_get(dev, "lltc,ctrl", 0);
  	if (IS_ERR(led_data->gpiod))
  		return PTR_ERR(led_data->gpiod);
  
  	child = device_get_next_child_node(dev, NULL);
  
  	fwnode_property_read_string(child, "linux,default-trigger",
  				    &led_data->cdev.default_trigger);
  
  	if (!fwnode_property_read_string(child, "default-state", &tmp)) {
  		if (!strcmp(tmp, "on"))
  			state = LEDS_GPIO_DEFSTATE_ON;
  	}
  
  	led_data->cdev.brightness_set_blocking = lt3593_led_set;
  	led_data->cdev.brightness = state ? LED_FULL : LED_OFF;
  
  	init_data.fwnode = child;
  	init_data.devicename = LED_LT3593_NAME;
  	init_data.default_label = ":";
  
  	ret = devm_led_classdev_register_ext(dev, &led_data->cdev, &init_data);
  	if (ret < 0) {
  		fwnode_handle_put(child);
  		return ret;
  	}
  
  	led_data->cdev.dev->of_node = dev->of_node;
  	platform_set_drvdata(pdev, led_data);
  
  	return 0;
  }
  
  static const struct of_device_id of_lt3593_leds_match[] = {
  	{ .compatible = "lltc,lt3593", },
  	{},
  };
  MODULE_DEVICE_TABLE(of, of_lt3593_leds_match);
  
  static struct platform_driver lt3593_led_driver = {
  	.probe		= lt3593_led_probe,
  	.driver		= {
  		.name	= "leds-lt3593",
  		.of_match_table = of_match_ptr(of_lt3593_leds_match),
  	},
  };
  
  module_platform_driver(lt3593_led_driver);
  
  MODULE_AUTHOR("Daniel Mack <daniel@zonque.org>");
  MODULE_DESCRIPTION("LED driver for LT3593 controllers");
  MODULE_LICENSE("GPL v2");
  MODULE_ALIAS("platform:leds-lt3593");
  