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"); 162