leds-atmel-pwm.c

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#include <linux/kernel.h>
#include <linux/platform_device.h>
#include <linux/leds.h>
#include <linux/io.h>
#include <linux/atmel_pwm.h>
#include <linux/slab.h>
#include <linux/module.h>


struct pwmled {
    struct led_classdev cdev;
    struct pwm_channel  pwmc;
    struct gpio_led     *desc;
    u32         mult;
    u8          active_low;
};


/*
 * For simplicity, we use "brightness" as if it were a linear function
 * of PWM duty cycle.  However, a logarithmic function of duty cycle is
 * probably a better match for perceived brightness: two is half as bright
 * as four, four is half as bright as eight, etc
 */
static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
{
    struct pwmled        *led;

    /* update the duty cycle for the *next* period */
    led = container_of(cdev, struct pwmled, cdev);
    pwm_channel_writel(&led->pwmc, PWM_CUPD, led->mult * (unsigned) b);
}

/*
 * NOTE:  we reuse the platform_data structure of GPIO leds,
 * but repurpose its "gpio" number as a PWM channel number.
 */
static int __devinit pwmled_probe(struct platform_device *pdev)
{
    const struct gpio_led_platform_data *pdata;
    struct pwmled               *leds;
    int                 i;
    int                 status;

    pdata = pdev->dev.platform_data;
    if (!pdata || pdata->num_leds < 1)
        return -ENODEV;

    leds = devm_kzalloc(&pdev->dev, pdata->num_leds * sizeof(*leds),
            GFP_KERNEL);
    if (!leds)
        return -ENOMEM;

    for (i = 0; i < pdata->num_leds; i++) {
        struct pwmled       *led = leds + i;
        const struct gpio_led   *dat = pdata->leds + i;
        u32         tmp;

        led->cdev.name = dat->name;
        led->cdev.brightness = LED_OFF;
        led->cdev.brightness_set = pwmled_brightness;
        led->cdev.default_trigger = dat->default_trigger;

        led->active_low = dat->active_low;

        status = pwm_channel_alloc(dat->gpio, &led->pwmc);
        if (status < 0)
            goto err;

        /*
         * Prescale clock by 2^x, so PWM counts in low MHz.
         * Start each cycle with the LED active, so increasing
         * the duty cycle gives us more time on (== brighter).
         */
        tmp = 5;
        if (!led->active_low)
            tmp |= PWM_CPR_CPOL;
        pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);

        /*
         * Pick a period so PWM cycles at 100+ Hz; and a multiplier
         * for scaling duty cycle:  brightness * mult.
         */
        tmp = (led->pwmc.mck / (1 << 5)) / 100;
        tmp /= 255;
        led->mult = tmp;
        pwm_channel_writel(&led->pwmc, PWM_CDTY,
                led->cdev.brightness * 255);
        pwm_channel_writel(&led->pwmc, PWM_CPRD,
                LED_FULL * tmp);

        pwm_channel_enable(&led->pwmc);

        /* Hand it over to the LED framework */
        status = led_classdev_register(&pdev->dev, &led->cdev);
        if (status < 0) {
            pwm_channel_free(&led->pwmc);
            goto err;
        }
    }

    platform_set_drvdata(pdev, leds);
    return 0;

err:
    if (i > 0) {
        for (i = i - 1; i >= 0; i--) {
            led_classdev_unregister(&leds[i].cdev);
            pwm_channel_free(&leds[i].pwmc);
        }
    }

    return status;
}

static int __exit pwmled_remove(struct platform_device *pdev)
{
    const struct gpio_led_platform_data *pdata;
    struct pwmled               *leds;
    unsigned                i;

    pdata = pdev->dev.platform_data;
    leds = platform_get_drvdata(pdev);

    for (i = 0; i < pdata->num_leds; i++) {
        struct pwmled       *led = leds + i;

        led_classdev_unregister(&led->cdev);
        pwm_channel_free(&led->pwmc);
    }

    platform_set_drvdata(pdev, NULL);
    return 0;
}

static struct platform_driver pwmled_driver = {
    .driver = {
        .name =     "leds-atmel-pwm",
        .owner =    THIS_MODULE,
    },
    /* REVISIT add suspend() and resume() methods */
    .probe =    pwmled_probe,
    .remove =   __exit_p(pwmled_remove),
};

module_platform_driver(pwmled_driver);

MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:leds-atmel-pwm");