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
  8
  9struct pwmled {
 10	struct led_classdev	cdev;
 11	struct pwm_channel	pwmc;
 12	struct gpio_led		*desc;
 13	u32			mult;
 14	u8			active_low;
 15};
 16
 17
 18/*
 19 * For simplicity, we use "brightness" as if it were a linear function
 20 * of PWM duty cycle.  However, a logarithmic function of duty cycle is
 21 * probably a better match for perceived brightness: two is half as bright
 22 * as four, four is half as bright as eight, etc
 23 */
 24static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
 25{
 26	struct pwmled		 *led;
 27
 28	/* update the duty cycle for the *next* period */
 29	led = container_of(cdev, struct pwmled, cdev);
 30	pwm_channel_writel(&led->pwmc, PWM_CUPD, led->mult * (unsigned) b);
 31}
 32
 33/*
 34 * NOTE:  we reuse the platform_data structure of GPIO leds,
 35 * but repurpose its "gpio" number as a PWM channel number.
 36 */
 37static int __init pwmled_probe(struct platform_device *pdev)
 38{
 39	const struct gpio_led_platform_data	*pdata;
 40	struct pwmled				*leds;
 41	int					i;
 42	int					status;
 43
 44	pdata = pdev->dev.platform_data;
 45	if (!pdata || pdata->num_leds < 1)
 46		return -ENODEV;
 47
 48	leds = kcalloc(pdata->num_leds, sizeof(*leds), GFP_KERNEL);
 49	if (!leds)
 50		return -ENOMEM;
 51
 52	for (i = 0; i < pdata->num_leds; i++) {
 53		struct pwmled		*led = leds + i;
 54		const struct gpio_led	*dat = pdata->leds + i;
 55		u32			tmp;
 56
 57		led->cdev.name = dat->name;
 58		led->cdev.brightness = LED_OFF;
 59		led->cdev.brightness_set = pwmled_brightness;
 60		led->cdev.default_trigger = dat->default_trigger;
 61
 62		led->active_low = dat->active_low;
 63
 64		status = pwm_channel_alloc(dat->gpio, &led->pwmc);
 65		if (status < 0)
 66			goto err;
 67
 68		/*
 69		 * Prescale clock by 2^x, so PWM counts in low MHz.
 70		 * Start each cycle with the LED active, so increasing
 71		 * the duty cycle gives us more time on (== brighter).
 72		 */
 73		tmp = 5;
 74		if (!led->active_low)
 75			tmp |= PWM_CPR_CPOL;
 76		pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
 77
 78		/*
 79		 * Pick a period so PWM cycles at 100+ Hz; and a multiplier
 80		 * for scaling duty cycle:  brightness * mult.
 81		 */
 82		tmp = (led->pwmc.mck / (1 << 5)) / 100;
 83		tmp /= 255;
 84		led->mult = tmp;
 85		pwm_channel_writel(&led->pwmc, PWM_CDTY,
 86				led->cdev.brightness * 255);
 87		pwm_channel_writel(&led->pwmc, PWM_CPRD,
 88				LED_FULL * tmp);
 89
 90		pwm_channel_enable(&led->pwmc);
 91
 92		/* Hand it over to the LED framework */
 93		status = led_classdev_register(&pdev->dev, &led->cdev);
 94		if (status < 0) {
 95			pwm_channel_free(&led->pwmc);
 96			goto err;
 97		}
 98	}
 99
100	platform_set_drvdata(pdev, leds);
101	return 0;
102
103err:
104	if (i > 0) {
105		for (i = i - 1; i >= 0; i--) {
106			led_classdev_unregister(&leds[i].cdev);
107			pwm_channel_free(&leds[i].pwmc);
108		}
109	}
110	kfree(leds);
111
112	return status;
113}
114
115static int __exit pwmled_remove(struct platform_device *pdev)
116{
117	const struct gpio_led_platform_data	*pdata;
118	struct pwmled				*leds;
119	unsigned				i;
120
121	pdata = pdev->dev.platform_data;
122	leds = platform_get_drvdata(pdev);
123
124	for (i = 0; i < pdata->num_leds; i++) {
125		struct pwmled		*led = leds + i;
126
127		led_classdev_unregister(&led->cdev);
128		pwm_channel_free(&led->pwmc);
129	}
130
131	kfree(leds);
132	platform_set_drvdata(pdev, NULL);
133	return 0;
134}
135
136/* work with hotplug and coldplug */
137MODULE_ALIAS("platform:leds-atmel-pwm");
138
139static struct platform_driver pwmled_driver = {
140	.driver = {
141		.name =		"leds-atmel-pwm",
142		.owner =	THIS_MODULE,
143	},
144	/* REVISIT add suspend() and resume() methods */
145	.remove =	__exit_p(pwmled_remove),
146};
147
148static int __init modinit(void)
149{
150	return platform_driver_probe(&pwmled_driver, pwmled_probe);
151}
152module_init(modinit);
153
154static void __exit modexit(void)
155{
156	platform_driver_unregister(&pwmled_driver);
157}
158module_exit(modexit);
159
160MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
161MODULE_LICENSE("GPL");