#include <linux/kernel.h>
  #include <linux/platform_device.h>
  #include <linux/leds.h>
  #include <linux/io.h>
  #include <linux/atmel_pwm.h>

  #include <linux/slab.h>

  #include <linux/module.h>

  
  
  struct pwmled {
  	struct led_classdev	cdev;
  	struct pwm_channel	pwmc;
  	struct gpio_led		*desc;
  	u32			mult;
  	u8			active_low;
  };
  
  
  /*
   * For simplicity, we use "brightness" as if it were a linear function
   * of PWM duty cycle.  However, a logarithmic function of duty cycle is
   * probably a better match for perceived brightness: two is half as bright
   * as four, four is half as bright as eight, etc
   */
  static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
  {
  	struct pwmled		 *led;
  
  	/* update the duty cycle for the *next* period */
  	led = container_of(cdev, struct pwmled, cdev);
  	pwm_channel_writel(&led->pwmc, PWM_CUPD, led->mult * (unsigned) b);
  }
  
  /*
   * NOTE:  we reuse the platform_data structure of GPIO leds,
   * but repurpose its "gpio" number as a PWM channel number.
   */
  static int __init pwmled_probe(struct platform_device *pdev)
  {
  	const struct gpio_led_platform_data	*pdata;
  	struct pwmled				*leds;

  	int					i;

  	int					status;
  
  	pdata = pdev->dev.platform_data;
  	if (!pdata || pdata->num_leds < 1)
  		return -ENODEV;
  
  	leds = kcalloc(pdata->num_leds, sizeof(*leds), GFP_KERNEL);
  	if (!leds)
  		return -ENOMEM;
  
  	for (i = 0; i < pdata->num_leds; i++) {
  		struct pwmled		*led = leds + i;
  		const struct gpio_led	*dat = pdata->leds + i;
  		u32			tmp;
  
  		led->cdev.name = dat->name;
  		led->cdev.brightness = LED_OFF;
  		led->cdev.brightness_set = pwmled_brightness;
  		led->cdev.default_trigger = dat->default_trigger;
  
  		led->active_low = dat->active_low;
  
  		status = pwm_channel_alloc(dat->gpio, &led->pwmc);
  		if (status < 0)
  			goto err;
  
  		/*
  		 * Prescale clock by 2^x, so PWM counts in low MHz.
  		 * Start each cycle with the LED active, so increasing
  		 * the duty cycle gives us more time on (== brighter).
  		 */
  		tmp = 5;
  		if (!led->active_low)
  			tmp |= PWM_CPR_CPOL;
  		pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
  
  		/*
  		 * Pick a period so PWM cycles at 100+ Hz; and a multiplier
  		 * for scaling duty cycle:  brightness * mult.
  		 */
  		tmp = (led->pwmc.mck / (1 << 5)) / 100;
  		tmp /= 255;
  		led->mult = tmp;
  		pwm_channel_writel(&led->pwmc, PWM_CDTY,
  				led->cdev.brightness * 255);
  		pwm_channel_writel(&led->pwmc, PWM_CPRD,
  				LED_FULL * tmp);
  
  		pwm_channel_enable(&led->pwmc);
  
  		/* Hand it over to the LED framework */
  		status = led_classdev_register(&pdev->dev, &led->cdev);
  		if (status < 0) {
  			pwm_channel_free(&led->pwmc);
  			goto err;
  		}
  	}
  
  	platform_set_drvdata(pdev, leds);
  	return 0;
  
  err:
  	if (i > 0) {
  		for (i = i - 1; i >= 0; i--) {
  			led_classdev_unregister(&leds[i].cdev);
  			pwm_channel_free(&leds[i].pwmc);
  		}
  	}
  	kfree(leds);
  
  	return status;
  }
  
  static int __exit pwmled_remove(struct platform_device *pdev)
  {
  	const struct gpio_led_platform_data	*pdata;
  	struct pwmled				*leds;
  	unsigned				i;
  
  	pdata = pdev->dev.platform_data;
  	leds = platform_get_drvdata(pdev);
  
  	for (i = 0; i < pdata->num_leds; i++) {
  		struct pwmled		*led = leds + i;
  
  		led_classdev_unregister(&led->cdev);
  		pwm_channel_free(&led->pwmc);
  	}
  
  	kfree(leds);
  	platform_set_drvdata(pdev, NULL);
  	return 0;
  }
  
  static struct platform_driver pwmled_driver = {
  	.driver = {
  		.name =		"leds-atmel-pwm",
  		.owner =	THIS_MODULE,
  	},
  	/* REVISIT add suspend() and resume() methods */

  	.probe =	pwmled_probe,

  	.remove =	__exit_p(pwmled_remove),
  };

  module_platform_driver(pwmled_driver);

  
  MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
  MODULE_LICENSE("GPL");

  MODULE_ALIAS("platform:leds-atmel-pwm");