LXR 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
   7
   8struct 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 */
  23static 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 */
  36static int __init pwmled_probe(struct platform_device *pdev)
  37{
  38        const struct gpio_led_platform_data     *pdata;
  39        struct pwmled                           *leds;
  40        int                                     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
 102err:
 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
 114static 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/* work with hotplug and coldplug */
 136MODULE_ALIAS("platform:leds-atmel-pwm");
 137
 138static struct platform_driver pwmled_driver = {
 139        .driver = {
 140                .name =         "leds-atmel-pwm",
 141                .owner =        THIS_MODULE,
 142        },
 143        /* REVISIT add suspend() and resume() methods */
 144        .remove =       __exit_p(pwmled_remove),
 145};
 146
 147static int __init modinit(void)
 148{
 149        return platform_driver_probe(&pwmled_driver, pwmled_probe);
 150}
 151module_init(modinit);
 152
 153static void __exit modexit(void)
 154{
 155        platform_driver_unregister(&pwmled_driver);
 156}
 157module_exit(modexit);
 158
 159MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
 160MODULE_LICENSE("GPL");
 161