drivers/leds/leds-atmel-pwm.c

   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  */
  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  */
  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
 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
 148 static int __init modinit(void)
 149 {
 150         return platform_driver_probe(&pwmled_driver, pwmled_probe);
 151 }
 152 module_init(modinit);
 153
 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");