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 #include <linux/module.h>
   8
   9
  10 struct pwmled {
  11         struct led_classdev     cdev;
  12         struct pwm_channel      pwmc;
  13         struct gpio_led         *desc;
  14         u32                     mult;
  15         u8                      active_low;
  16 };
  17
  18
  19 /*
  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
  24  */
  25 static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
  26 {
  27         struct pwmled            *led;
  28
  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);
  32 }
  33
  34 /*
  35  * NOTE:  we reuse the platform_data structure of GPIO leds,
  36  * but repurpose its "gpio" number as a PWM channel number.
  37  */
  38 static int pwmled_probe(struct platform_device *pdev)
  39 {
  40         const struct gpio_led_platform_data     *pdata;
  41         struct pwmled                           *leds;
  42         int                                     i;
  43         int                                     status;
  44
  45         pdata = dev_get_platdata(&pdev->dev);
  46         if (!pdata || pdata->num_leds < 1)
  47                 return -ENODEV;
  48
  49         leds = devm_kzalloc(&pdev->dev, pdata->num_leds * sizeof(*leds),
  50                         GFP_KERNEL);
  51         if (!leds)
  52                 return -ENOMEM;
  53
  54         for (i = 0; i < pdata->num_leds; i++) {
  55                 struct pwmled           *led = leds + i;
  56                 const struct gpio_led   *dat = pdata->leds + i;
  57                 u32                     tmp;
  58
  59                 led->cdev.name = dat->name;
  60                 led->cdev.brightness = LED_OFF;
  61                 led->cdev.brightness_set = pwmled_brightness;
  62                 led->cdev.default_trigger = dat->default_trigger;
  63
  64                 led->active_low = dat->active_low;
  65
  66                 status = pwm_channel_alloc(dat->gpio, &led->pwmc);
  67                 if (status < 0)
  68                         goto err;
  69
  70                 /*
  71                  * Prescale clock by 2^x, so PWM counts in low MHz.
  72                  * Start each cycle with the LED active, so increasing
  73                  * the duty cycle gives us more time on (== brighter).
  74                  */
  75                 tmp = 5;
  76                 if (!led->active_low)
  77                         tmp |= PWM_CPR_CPOL;
  78                 pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
  79
  80                 /*
  81                  * Pick a period so PWM cycles at 100+ Hz; and a multiplier
  82                  * for scaling duty cycle:  brightness * mult.
  83                  */
  84                 tmp = (led->pwmc.mck / (1 << 5)) / 100;
  85                 tmp /= 255;
  86                 led->mult = tmp;
  87                 pwm_channel_writel(&led->pwmc, PWM_CDTY,
  88                                 led->cdev.brightness * 255);
  89                 pwm_channel_writel(&led->pwmc, PWM_CPRD,
  90                                 LED_FULL * tmp);
  91
  92                 pwm_channel_enable(&led->pwmc);
  93
  94                 /* Hand it over to the LED framework */
  95                 status = led_classdev_register(&pdev->dev, &led->cdev);
  96                 if (status < 0) {
  97                         pwm_channel_free(&led->pwmc);
  98                         goto err;
  99                 }
 100         }
 101
 102         platform_set_drvdata(pdev, leds);
 103         return 0;
 104
 105 err:
 106         if (i > 0) {
 107                 for (i = i - 1; i >= 0; i--) {
 108                         led_classdev_unregister(&leds[i].cdev);
 109                         pwm_channel_free(&leds[i].pwmc);
 110                 }
 111         }
 112
 113         return status;
 114 }
 115
 116 static int pwmled_remove(struct platform_device *pdev)
 117 {
 118         const struct gpio_led_platform_data     *pdata;
 119         struct pwmled                           *leds;
 120         unsigned                                i;
 121
 122         pdata = dev_get_platdata(&pdev->dev);
 123         leds = platform_get_drvdata(pdev);
 124
 125         for (i = 0; i < pdata->num_leds; i++) {
 126                 struct pwmled           *led = leds + i;
 127
 128                 led_classdev_unregister(&led->cdev);
 129                 pwm_channel_free(&led->pwmc);
 130         }
 131
 132         return 0;
 133 }
 134
 135 static struct platform_driver pwmled_driver = {
 136         .driver = {
 137                 .name =         "leds-atmel-pwm",
 138                 .owner =        THIS_MODULE,
 139         },
 140         /* REVISIT add suspend() and resume() methods */
 141         .probe =        pwmled_probe,
 142         .remove =       pwmled_remove,
 143 };
 144
 145 module_platform_driver(pwmled_driver);
 146
 147 MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
 148 MODULE_LICENSE("GPL");
 149 MODULE_ALIAS("platform:leds-atmel-pwm");