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Linux/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");
150 

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