1 #include <linux/kernel.h>
2 #include <linux/platform_device.h>
3 #include <linux/leds.h>
5 #include <linux/atmel_pwm.h>
6 #include <linux/slab.h>
7 #include <linux/module.h>
11 struct led_classdev cdev;
12 struct pwm_channel pwmc;
13 struct gpio_led *desc;
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
25 static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
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);
35 * NOTE: we reuse the platform_data structure of GPIO leds,
36 * but repurpose its "gpio" number as a PWM channel number.
38 static int __init pwmled_probe(struct platform_device *pdev)
40 const struct gpio_led_platform_data *pdata;
45 pdata = pdev->dev.platform_data;
46 if (!pdata || pdata->num_leds < 1)
49 leds = kcalloc(pdata->num_leds, sizeof(*leds), GFP_KERNEL);
53 for (i = 0; i < pdata->num_leds; i++) {
54 struct pwmled *led = leds + i;
55 const struct gpio_led *dat = pdata->leds + i;
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;
63 led->active_low = dat->active_low;
65 status = pwm_channel_alloc(dat->gpio, &led->pwmc);
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).
77 pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
80 * Pick a period so PWM cycles at 100+ Hz; and a multiplier
81 * for scaling duty cycle: brightness * mult.
83 tmp = (led->pwmc.mck / (1 << 5)) / 100;
86 pwm_channel_writel(&led->pwmc, PWM_CDTY,
87 led->cdev.brightness * 255);
88 pwm_channel_writel(&led->pwmc, PWM_CPRD,
91 pwm_channel_enable(&led->pwmc);
93 /* Hand it over to the LED framework */
94 status = led_classdev_register(&pdev->dev, &led->cdev);
96 pwm_channel_free(&led->pwmc);
101 platform_set_drvdata(pdev, leds);
106 for (i = i - 1; i >= 0; i--) {
107 led_classdev_unregister(&leds[i].cdev);
108 pwm_channel_free(&leds[i].pwmc);
116 static int __exit pwmled_remove(struct platform_device *pdev)
118 const struct gpio_led_platform_data *pdata;
122 pdata = pdev->dev.platform_data;
123 leds = platform_get_drvdata(pdev);
125 for (i = 0; i < pdata->num_leds; i++) {
126 struct pwmled *led = leds + i;
128 led_classdev_unregister(&led->cdev);
129 pwm_channel_free(&led->pwmc);
133 platform_set_drvdata(pdev, NULL);
137 static struct platform_driver pwmled_driver = {
139 .name = "leds-atmel-pwm",
140 .owner = THIS_MODULE,
142 /* REVISIT add suspend() and resume() methods */
143 .probe = pwmled_probe,
144 .remove = __exit_p(pwmled_remove),
147 module_platform_driver(pwmled_driver);
149 MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
150 MODULE_LICENSE("GPL");
151 MODULE_ALIAS("platform:leds-atmel-pwm");