linux/drivers/leds/leds-atmel-pwm.c
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   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
  10struct 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 */
  25static 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 */
  38static 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 = pdev->dev.platform_data;
  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
 105err:
 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
 116static 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 = pdev->dev.platform_data;
 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        platform_set_drvdata(pdev, NULL);
 133        return 0;
 134}
 135
 136static struct platform_driver pwmled_driver = {
 137        .driver = {
 138                .name =         "leds-atmel-pwm",
 139                .owner =        THIS_MODULE,
 140        },
 141        /* REVISIT add suspend() and resume() methods */
 142        .probe =        pwmled_probe,
 143        .remove =       pwmled_remove,
 144};
 145
 146module_platform_driver(pwmled_driver);
 147
 148MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
 149MODULE_LICENSE("GPL");
 150MODULE_ALIAS("platform:leds-atmel-pwm");
 151
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