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
9 struct 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 */
pwmled_brightness(struct led_classdev * cdev,enum led_brightness b)24 static 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 */
pwmled_probe(struct platform_device * pdev)37 static 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
103 err:
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
pwmled_remove(struct platform_device * pdev)115 static 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 */
137 MODULE_ALIAS("platform:leds-atmel-pwm");
138
139 static 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
modinit(void)148 static int __init modinit(void)
149 {
150 return platform_driver_probe(&pwmled_driver, pwmled_probe);
151 }
152 module_init(modinit);
153
modexit(void)154 static void __exit modexit(void)
155 {
156 platform_driver_unregister(&pwmled_driver);
157 }
158 module_exit(modexit);
159
160 MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
161 MODULE_LICENSE("GPL");
162