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 __devinit 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 = pdev->dev.platform_data;
 46	if (!pdata || pdata->num_leds < 1)
 47		return -ENODEV;
 48
 49	leds = kcalloc(pdata->num_leds, sizeof(*leds), GFP_KERNEL);
 50	if (!leds)
 51		return -ENOMEM;
 52
 53	for (i = 0; i < pdata->num_leds; i++) {
 54		struct pwmled		*led = leds + i;
 55		const struct gpio_led	*dat = pdata->leds + i;
 56		u32			tmp;
 57
 58		led->cdev.name = dat->name;
 59		led->cdev.brightness = LED_OFF;
 60		led->cdev.brightness_set = pwmled_brightness;
 61		led->cdev.default_trigger = dat->default_trigger;
 62
 63		led->active_low = dat->active_low;
 64
 65		status = pwm_channel_alloc(dat->gpio, &led->pwmc);
 66		if (status < 0)
 67			goto err;
 68
 69		/*
 70		 * Prescale clock by 2^x, so PWM counts in low MHz.
 71		 * Start each cycle with the LED active, so increasing
 72		 * the duty cycle gives us more time on (== brighter).
 73		 */
 74		tmp = 5;
 75		if (!led->active_low)
 76			tmp |= PWM_CPR_CPOL;
 77		pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
 78
 79		/*
 80		 * Pick a period so PWM cycles at 100+ Hz; and a multiplier
 81		 * for scaling duty cycle:  brightness * mult.
 82		 */
 83		tmp = (led->pwmc.mck / (1 << 5)) / 100;
 84		tmp /= 255;
 85		led->mult = tmp;
 86		pwm_channel_writel(&led->pwmc, PWM_CDTY,
 87				led->cdev.brightness * 255);
 88		pwm_channel_writel(&led->pwmc, PWM_CPRD,
 89				LED_FULL * tmp);
 90
 91		pwm_channel_enable(&led->pwmc);
 92
 93		/* Hand it over to the LED framework */
 94		status = led_classdev_register(&pdev->dev, &led->cdev);
 95		if (status < 0) {
 96			pwm_channel_free(&led->pwmc);
 97			goto err;
 98		}
 99	}
100
101	platform_set_drvdata(pdev, leds);
102	return 0;
103
104err:
105	if (i > 0) {
106		for (i = i - 1; i >= 0; i--) {
107			led_classdev_unregister(&leds[i].cdev);
108			pwm_channel_free(&leds[i].pwmc);
109		}
110	}
111	kfree(leds);
112
113	return status;
114}
115
116static int __exit 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 = pdev->dev.platform_data;
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	kfree(leds);
133	platform_set_drvdata(pdev, NULL);
134	return 0;
135}
136
137static struct platform_driver pwmled_driver = {
138	.driver = {
139		.name =		"leds-atmel-pwm",
140		.owner =	THIS_MODULE,
141	},
142	/* REVISIT add suspend() and resume() methods */
143	.probe =	pwmled_probe,
144	.remove =	__exit_p(pwmled_remove),
145};
146
147module_platform_driver(pwmled_driver);
148
149MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
150MODULE_LICENSE("GPL");
151MODULE_ALIAS("platform:leds-atmel-pwm");