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 pwmled_probe(struct platform_device *pdev)
{
const struct gpio_led_platform_data *pdata;
struct pwmled *leds;
int i;
int status;
pdata = dev_get_platdata(&pdev->dev);
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 pwmled_remove(struct platform_device *pdev)
{
const struct gpio_led_platform_data *pdata;
struct pwmled *leds;
unsigned i;
pdata = dev_get_platdata(&pdev->dev);
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);
}
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 = 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");