1#include <linux/kernel.h>
  2#include <linux/platform_device.h>
  3#include <linux/leds.h>
  4#include <linux/io.h>
  5#include <linux/atmel_pwm.h>
  6#include <linux/slab.h>
  7#include <linux/module.h>
  8
  9
 10struct pwmled {
 11	struct led_classdev	cdev;
 12	struct pwm_channel	pwmc;
 13	struct gpio_led		*desc;
 14	u32			mult;
 15	u8			active_low;
 16};
 17
 18
 19/*
 20 * For simplicity, we use "brightness" as if it were a linear function
 21 * of PWM duty cycle.  However, a logarithmic function of duty cycle is
 22 * probably a better match for perceived brightness: two is half as bright
 23 * as four, four is half as bright as eight, etc
 24 */
 25static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
 26{
 27	struct pwmled		 *led;
 28
 29	/* update the duty cycle for the *next* period */
 30	led = container_of(cdev, struct pwmled, cdev);
 31	pwm_channel_writel(&led->pwmc, PWM_CUPD, led->mult * (unsigned) b);
 32}
 33
 34/*
 35 * NOTE:  we reuse the platform_data structure of GPIO leds,
 36 * but repurpose its "gpio" number as a PWM channel number.
 37 */
 38static int pwmled_probe(struct platform_device *pdev)
 39{
 40	const struct gpio_led_platform_data	*pdata;
 41	struct pwmled				*leds;
 42	int					i;
 43	int					status;
 44
 45	pdata = dev_get_platdata(&pdev->dev);
 46	if (!pdata || pdata->num_leds < 1)
 47		return -ENODEV;
 48
 49	leds = devm_kzalloc(&pdev->dev, pdata->num_leds * sizeof(*leds),
 50			GFP_KERNEL);
 51	if (!leds)
 52		return -ENOMEM;
 53
 54	for (i = 0; i < pdata->num_leds; i++) {
 55		struct pwmled		*led = leds + i;
 56		const struct gpio_led	*dat = pdata->leds + i;
 57		u32			tmp;
 58
 59		led->cdev.name = dat->name;
 60		led->cdev.brightness = LED_OFF;
 61		led->cdev.brightness_set = pwmled_brightness;
 62		led->cdev.default_trigger = dat->default_trigger;
 63
 64		led->active_low = dat->active_low;
 65
 66		status = pwm_channel_alloc(dat->gpio, &led->pwmc);
 67		if (status < 0)
 68			goto err;
 69
 70		/*
 71		 * Prescale clock by 2^x, so PWM counts in low MHz.
 72		 * Start each cycle with the LED active, so increasing
 73		 * the duty cycle gives us more time on (== brighter).
 74		 */
 75		tmp = 5;
 76		if (!led->active_low)
 77			tmp |= PWM_CPR_CPOL;
 78		pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
 79
 80		/*
 81		 * Pick a period so PWM cycles at 100+ Hz; and a multiplier
 82		 * for scaling duty cycle:  brightness * mult.
 83		 */
 84		tmp = (led->pwmc.mck / (1 << 5)) / 100;
 85		tmp /= 255;
 86		led->mult = tmp;
 87		pwm_channel_writel(&led->pwmc, PWM_CDTY,
 88				led->cdev.brightness * 255);
 89		pwm_channel_writel(&led->pwmc, PWM_CPRD,
 90				LED_FULL * tmp);
 91
 92		pwm_channel_enable(&led->pwmc);
 93
 94		/* Hand it over to the LED framework */
 95		status = led_classdev_register(&pdev->dev, &led->cdev);
 96		if (status < 0) {
 97			pwm_channel_free(&led->pwmc);
 98			goto err;
 99		}
100	}
101
102	platform_set_drvdata(pdev, leds);
103	return 0;
104
105err:
106	if (i > 0) {
107		for (i = i - 1; i >= 0; i--) {
108			led_classdev_unregister(&leds[i].cdev);
109			pwm_channel_free(&leds[i].pwmc);
110		}
111	}
112
113	return status;
114}
115
116static int pwmled_remove(struct platform_device *pdev)
117{
118	const struct gpio_led_platform_data	*pdata;
119	struct pwmled				*leds;
120	unsigned				i;
121
122	pdata = dev_get_platdata(&pdev->dev);
123	leds = platform_get_drvdata(pdev);
124
125	for (i = 0; i < pdata->num_leds; i++) {
126		struct pwmled		*led = leds + i;
127
128		led_classdev_unregister(&led->cdev);
129		pwm_channel_free(&led->pwmc);
130	}
131
132	return 0;
133}
134
135static struct platform_driver pwmled_driver = {
136	.driver = {
137		.name =		"leds-atmel-pwm",
138		.owner =	THIS_MODULE,
139	},
140	/* REVISIT add suspend() and resume() methods */
141	.probe =	pwmled_probe,
142	.remove =	pwmled_remove,
143};
144
145module_platform_driver(pwmled_driver);
146
147MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
148MODULE_LICENSE("GPL");
149MODULE_ALIAS("platform:leds-atmel-pwm");