diff options
Diffstat (limited to 'drivers/leds/leds-atmel-pwm.c')
| -rw-r--r-- | drivers/leds/leds-atmel-pwm.c | 157 |
1 files changed, 157 insertions, 0 deletions
diff --git a/drivers/leds/leds-atmel-pwm.c b/drivers/leds/leds-atmel-pwm.c new file mode 100644 index 00000000000..af61f55571f --- /dev/null +++ b/drivers/leds/leds-atmel-pwm.c @@ -0,0 +1,157 @@ +#include <linux/kernel.h> +#include <linux/platform_device.h> +#include <linux/leds.h> +#include <linux/io.h> +#include <linux/atmel_pwm.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 __init pwmled_probe(struct platform_device *pdev) +{ + const struct gpio_led_platform_data *pdata; + struct pwmled *leds; + unsigned i; + int status; + + pdata = pdev->dev.platform_data; + if (!pdata || pdata->num_leds < 1) + return -ENODEV; + + leds = kcalloc(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); + } + } + kfree(leds); + + 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); + } + + kfree(leds); + 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 */ + .remove = __exit_p(pwmled_remove), +}; + +static int __init modinit(void) +{ + return platform_driver_probe(&pwmled_driver, pwmled_probe); +} +module_init(modinit); + +static void __exit modexit(void) +{ + platform_driver_unregister(&pwmled_driver); +} +module_exit(modexit); + +MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness"); +MODULE_LICENSE("GPL"); |