tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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
7
8struct pwmled {
9 struct led_classdev cdev;
10 struct pwm_channel pwmc;
11 struct gpio_led *desc;
12 u32 mult;
13 u8 active_low;
14};
15
16
17/*
18 * For simplicity, we use "brightness" as if it were a linear function
19 * of PWM duty cycle. However, a logarithmic function of duty cycle is
20 * probably a better match for perceived brightness: two is half as bright
21 * as four, four is half as bright as eight, etc
22 */
23static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
24{
25 struct pwmled *led;
26
27 /* update the duty cycle for the *next* period */
28 led = container_of(cdev, struct pwmled, cdev);
29 pwm_channel_writel(&led->pwmc, PWM_CUPD, led->mult * (unsigned) b);
30}
31
32/*
33 * NOTE: we reuse the platform_data structure of GPIO leds,
34 * but repurpose its "gpio" number as a PWM channel number.
35 */
36static int __init pwmled_probe(struct platform_device *pdev)
37{
38 const struct gpio_led_platform_data *pdata;
39 struct pwmled *leds;
40 unsigned i;
41 int status;
42
43 pdata = pdev->dev.platform_data;
44 if (!pdata || pdata->num_leds < 1)
45 return -ENODEV;
46
47 leds = kcalloc(pdata->num_leds, sizeof(*leds), GFP_KERNEL);
48 if (!leds)
49 return -ENOMEM;
50
51 for (i = 0; i < pdata->num_leds; i++) {
52 struct pwmled *led = leds + i;
53 const struct gpio_led *dat = pdata->leds + i;
54 u32 tmp;
55
56 led->cdev.name = dat->name;
57 led->cdev.brightness = LED_OFF;
58 led->cdev.brightness_set = pwmled_brightness;
59 led->cdev.default_trigger = dat->default_trigger;
60
61 led->active_low = dat->active_low;
62
63 status = pwm_channel_alloc(dat->gpio, &led->pwmc);
64 if (status < 0)
65 goto err;
66
67 /*
68 * Prescale clock by 2^x, so PWM counts in low MHz.
69 * Start each cycle with the LED active, so increasing
70 * the duty cycle gives us more time on (== brighter).
71 */
72 tmp = 5;
73 if (!led->active_low)
74 tmp |= PWM_CPR_CPOL;
75 pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
76
77 /*
78 * Pick a period so PWM cycles at 100+ Hz; and a multiplier
79 * for scaling duty cycle: brightness * mult.
80 */
81 tmp = (led->pwmc.mck / (1 << 5)) / 100;
82 tmp /= 255;
83 led->mult = tmp;
84 pwm_channel_writel(&led->pwmc, PWM_CDTY,
85 led->cdev.brightness * 255);
86 pwm_channel_writel(&led->pwmc, PWM_CPRD,
87 LED_FULL * tmp);
88
89 pwm_channel_enable(&led->pwmc);
90
91 /* Hand it over to the LED framework */
92 status = led_classdev_register(&pdev->dev, &led->cdev);
93 if (status < 0) {
94 pwm_channel_free(&led->pwmc);
95 goto err;
96 }
97 }
98
99 platform_set_drvdata(pdev, leds);
100 return 0;
101
102err:
103 if (i > 0) {
104 for (i = i - 1; i >= 0; i--) {
105 led_classdev_unregister(&leds[i].cdev);
106 pwm_channel_free(&leds[i].pwmc);
107 }
108 }
109 kfree(leds);
110
111 return status;
112}
113
114static int __exit pwmled_remove(struct platform_device *pdev)
115{
116 const struct gpio_led_platform_data *pdata;
117 struct pwmled *leds;
118 unsigned i;
119
120 pdata = pdev->dev.platform_data;
121 leds = platform_get_drvdata(pdev);
122
123 for (i = 0; i < pdata->num_leds; i++) {
124 struct pwmled *led = leds + i;
125
126 led_classdev_unregister(&led->cdev);
127 pwm_channel_free(&led->pwmc);
128 }
129
130 kfree(leds);
131 platform_set_drvdata(pdev, NULL);
132 return 0;
133}
134
135/* work with hotplug and coldplug */
136MODULE_ALIAS("platform:leds-atmel-pwm");
137
138static struct platform_driver pwmled_driver = {
139 .driver = {
140 .name = "leds-atmel-pwm",
141 .owner = THIS_MODULE,
142 },
143 /* REVISIT add suspend() and resume() methods */
144 .remove = __exit_p(pwmled_remove),
145};
146
147static int __init modinit(void)
148{
149 return platform_driver_probe(&pwmled_driver, pwmled_probe);
150}
151module_init(modinit);
152
153static void __exit modexit(void)
154{
155 platform_driver_unregister(&pwmled_driver);
156}
157module_exit(modexit);
158
159MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
160MODULE_LICENSE("GPL");