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
   7
   8 struct 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  */
  23 static 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  */
  36 static 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
 102 err:
 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
 114 static 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 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         .remove =       __exit_p(pwmled_remove),
 142 };
 143
 144 static int __init modinit(void)
 145 {
 146         return platform_driver_probe(&pwmled_driver, pwmled_probe);
 147 }
 148 module_init(modinit);
 149
 150 static void __exit modexit(void)
 151 {
 152         platform_driver_unregister(&pwmled_driver);
 153 }
 154 module_exit(modexit);
 155
 156 MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
 157 MODULE_LICENSE("GPL");