150 lines
3.5 KiB
C
150 lines
3.5 KiB
C
#include <linux/kernel.h>
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#include <linux/platform_device.h>
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#include <linux/leds.h>
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#include <linux/io.h>
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#include <linux/atmel_pwm.h>
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#include <linux/slab.h>
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#include <linux/module.h>
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struct pwmled {
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struct led_classdev cdev;
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struct pwm_channel pwmc;
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struct gpio_led *desc;
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u32 mult;
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u8 active_low;
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};
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/*
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* For simplicity, we use "brightness" as if it were a linear function
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* of PWM duty cycle. However, a logarithmic function of duty cycle is
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* probably a better match for perceived brightness: two is half as bright
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* as four, four is half as bright as eight, etc
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*/
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static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
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{
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struct pwmled *led;
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/* update the duty cycle for the *next* period */
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led = container_of(cdev, struct pwmled, cdev);
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pwm_channel_writel(&led->pwmc, PWM_CUPD, led->mult * (unsigned) b);
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}
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/*
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* NOTE: we reuse the platform_data structure of GPIO leds,
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* but repurpose its "gpio" number as a PWM channel number.
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*/
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static int pwmled_probe(struct platform_device *pdev)
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{
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const struct gpio_led_platform_data *pdata;
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struct pwmled *leds;
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int i;
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int status;
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pdata = pdev->dev.platform_data;
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if (!pdata || pdata->num_leds < 1)
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return -ENODEV;
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leds = devm_kzalloc(&pdev->dev, pdata->num_leds * sizeof(*leds),
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GFP_KERNEL);
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if (!leds)
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return -ENOMEM;
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for (i = 0; i < pdata->num_leds; i++) {
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struct pwmled *led = leds + i;
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const struct gpio_led *dat = pdata->leds + i;
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u32 tmp;
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led->cdev.name = dat->name;
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led->cdev.brightness = LED_OFF;
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led->cdev.brightness_set = pwmled_brightness;
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led->cdev.default_trigger = dat->default_trigger;
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led->active_low = dat->active_low;
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status = pwm_channel_alloc(dat->gpio, &led->pwmc);
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if (status < 0)
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goto err;
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/*
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* Prescale clock by 2^x, so PWM counts in low MHz.
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* Start each cycle with the LED active, so increasing
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* the duty cycle gives us more time on (== brighter).
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*/
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tmp = 5;
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if (!led->active_low)
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tmp |= PWM_CPR_CPOL;
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pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
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/*
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* Pick a period so PWM cycles at 100+ Hz; and a multiplier
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* for scaling duty cycle: brightness * mult.
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*/
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tmp = (led->pwmc.mck / (1 << 5)) / 100;
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tmp /= 255;
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led->mult = tmp;
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pwm_channel_writel(&led->pwmc, PWM_CDTY,
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led->cdev.brightness * 255);
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pwm_channel_writel(&led->pwmc, PWM_CPRD,
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LED_FULL * tmp);
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pwm_channel_enable(&led->pwmc);
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/* Hand it over to the LED framework */
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status = led_classdev_register(&pdev->dev, &led->cdev);
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if (status < 0) {
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pwm_channel_free(&led->pwmc);
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goto err;
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}
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}
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platform_set_drvdata(pdev, leds);
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return 0;
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err:
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if (i > 0) {
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for (i = i - 1; i >= 0; i--) {
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led_classdev_unregister(&leds[i].cdev);
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pwm_channel_free(&leds[i].pwmc);
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}
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}
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return status;
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}
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static int pwmled_remove(struct platform_device *pdev)
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{
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const struct gpio_led_platform_data *pdata;
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struct pwmled *leds;
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unsigned i;
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pdata = pdev->dev.platform_data;
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leds = platform_get_drvdata(pdev);
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for (i = 0; i < pdata->num_leds; i++) {
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struct pwmled *led = leds + i;
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led_classdev_unregister(&led->cdev);
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pwm_channel_free(&led->pwmc);
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}
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return 0;
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}
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static struct platform_driver pwmled_driver = {
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.driver = {
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.name = "leds-atmel-pwm",
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.owner = THIS_MODULE,
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},
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/* REVISIT add suspend() and resume() methods */
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.probe = pwmled_probe,
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.remove = pwmled_remove,
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};
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module_platform_driver(pwmled_driver);
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MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS("platform:leds-atmel-pwm");
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