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#include <linux/slab.h>
   7
   8
   9struct pwmled {
  10        struct led_classdev     cdev;
  11        struct pwm_channel      pwmc;
  12        struct gpio_led         *desc;
  13        u32                     mult;
  14        u8                      active_low;
  15};
  16
  17
  18/*
  19 * For simplicity, we use "brightness" as if it were a linear function
  20 * of PWM duty cycle.  However, a logarithmic function of duty cycle is
  21 * probably a better match for perceived brightness: two is half as bright
  22 * as four, four is half as bright as eight, etc
  23 */
  24static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
  25{
  26        struct pwmled            *led;
  27
  28        /* update the duty cycle for the *next* period */
  29        led = container_of(cdev, struct pwmled, cdev);
  30        pwm_channel_writel(&led->pwmc, PWM_CUPD, led->mult * (unsigned) b);
  31}
  32
  33/*
  34 * NOTE:  we reuse the platform_data structure of GPIO leds,
  35 * but repurpose its "gpio" number as a PWM channel number.
  36 */
  37static int __init pwmled_probe(struct platform_device *pdev)
  38{
  39        const struct gpio_led_platform_data     *pdata;
  40        struct pwmled                           *leds;
  41        int                                     i;
  42        int                                     status;
  43
  44        pdata = pdev->dev.platform_data;
  45        if (!pdata || pdata->num_leds < 1)
  46                return -ENODEV;
  47
  48        leds = kcalloc(pdata->num_leds, sizeof(*leds), GFP_KERNEL);
  49        if (!leds)
  50                return -ENOMEM;
  51
  52        for (i = 0; i < pdata->num_leds; i++) {
  53                struct pwmled           *led = leds + i;
  54                const struct gpio_led   *dat = pdata->leds + i;
  55                u32                     tmp;
  56
  57                led->cdev.name = dat->name;
  58                led->cdev.brightness = LED_OFF;
  59                led->cdev.brightness_set = pwmled_brightness;
  60                led->cdev.default_trigger = dat->default_trigger;
  61
  62                led->active_low = dat->active_low;
  63
  64                status = pwm_channel_alloc(dat->gpio, &led->pwmc);
  65                if (status < 0)
  66                        goto err;
  67
  68                /*
  69                 * Prescale clock by 2^x, so PWM counts in low MHz.
  70                 * Start each cycle with the LED active, so increasing
  71                 * the duty cycle gives us more time on (== brighter).
  72                 */
  73                tmp = 5;
  74                if (!led->active_low)
  75                        tmp |= PWM_CPR_CPOL;
  76                pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
  77
  78                /*
  79                 * Pick a period so PWM cycles at 100+ Hz; and a multiplier
  80                 * for scaling duty cycle:  brightness * mult.
  81                 */
  82                tmp = (led->pwmc.mck / (1 << 5)) / 100;
  83                tmp /= 255;
  84                led->mult = tmp;
  85                pwm_channel_writel(&led->pwmc, PWM_CDTY,
  86                                led->cdev.brightness * 255);
  87                pwm_channel_writel(&led->pwmc, PWM_CPRD,
  88                                LED_FULL * tmp);
  89
  90                pwm_channel_enable(&led->pwmc);
  91
  92                /* Hand it over to the LED framework */
  93                status = led_classdev_register(&pdev->dev, &led->cdev);
  94                if (status < 0) {
  95                        pwm_channel_free(&led->pwmc);
  96                        goto err;
  97                }
  98        }
  99
 100        platform_set_drvdata(pdev, leds);
 101        return 0;
 102
 103err:
 104        if (i > 0) {
 105                for (i = i - 1; i >= 0; i--) {
 106                        led_classdev_unregister(&leds[i].cdev);
 107                        pwm_channel_free(&leds[i].pwmc);
 108                }
 109        }
 110        kfree(leds);
 111
 112        return status;
 113}
 114
 115static int __exit pwmled_remove(struct platform_device *pdev)
 116{
 117        const struct gpio_led_platform_data     *pdata;
 118        struct pwmled                           *leds;
 119        unsigned                                i;
 120
 121        pdata = pdev->dev.platform_data;
 122        leds = platform_get_drvdata(pdev);
 123
 124        for (i = 0; i < pdata->num_leds; i++) {
 125                struct pwmled           *led = leds + i;
 126
 127                led_classdev_unregister(&led->cdev);
 128                pwm_channel_free(&led->pwmc);
 129        }
 130
 131        kfree(leds);
 132        platform_set_drvdata(pdev, NULL);
 133        return 0;
 134}
 135
 136/* work with hotplug and coldplug */
 137MODULE_ALIAS("platform:leds-atmel-pwm");
 138
 139static struct platform_driver pwmled_driver = {
 140        .driver = {
 141                .name =         "leds-atmel-pwm",
 142                .owner =        THIS_MODULE,
 143        },
 144        /* REVISIT add suspend() and resume() methods */
 145        .remove =       __exit_p(pwmled_remove),
 146};
 147
 148static int __init modinit(void)
 149{
 150        return platform_driver_probe(&pwmled_driver, pwmled_probe);
 151}
 152module_init(modinit);
 153
 154static void __exit modexit(void)
 155{
 156        platform_driver_unregister(&pwmled_driver);
 157}
 158module_exit(modexit);
 159
 160MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
 161MODULE_LICENSE("GPL");
 162