diff options
author | David Brownell <david-b@pacbell.net> | 2008-02-08 12:21:22 (GMT) |
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committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-02-08 17:22:38 (GMT) |
commit | de5c9edee7a3cfdc6dd1a31c4794dc41ef3c70f9 (patch) | |
tree | 2cc474aa124cd9efb8aa5b96072dd3fd2325148b /drivers | |
parent | 9a1e8eb1f0b76b5e72a2343ad881c81b08dd6410 (diff) | |
download | linux-fsl-qoriq-de5c9edee7a3cfdc6dd1a31c4794dc41ef3c70f9.tar.xz |
PWM LED driver
This is a LED driver using the PWM on newer SOCs from Atmel; brightness is
controlled by changing the PWM duty cycle. So for example if you've set up
two leds labeled "pwm0" and "pwm1":
echo 0 > /sys/class/leds/pwm2/brightness # off (0%)
echo 80 > /sys/class/leds/pwm2/brightness
echo 255 > /sys/class/leds/pwm2/brightness # on (100%)
Note that "brightness" here isn't linear; maybe that should change. Going
from 4 to 8 probably doubles perceived brightness, while 244 to 248 is
imperceptible.
This is mostly intended to be a simple example of PWM, although it's
realistic since LCD backlights are often driven with PWM to conserve
battery power (and offer brightness options).
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Andrew Victor <linux@maxim.org.za>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/leds/Kconfig | 7 | ||||
-rw-r--r-- | drivers/leds/Makefile | 1 | ||||
-rw-r--r-- | drivers/leds/leds-atmel-pwm.c | 157 |
3 files changed, 165 insertions, 0 deletions
diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig index 851a3b0..859814f 100644 --- a/drivers/leds/Kconfig +++ b/drivers/leds/Kconfig @@ -18,6 +18,13 @@ config LEDS_CLASS comment "LED drivers" +config LEDS_ATMEL_PWM + tristate "LED Support using Atmel PWM outputs" + depends on LEDS_CLASS && ATMEL_PWM + help + This option enables support for LEDs driven using outputs + of the dedicated PWM controller found on newer Atmel SOCs. + config LEDS_CORGI tristate "LED Support for the Sharp SL-C7x0 series" depends on LEDS_CLASS && PXA_SHARP_C7xx diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile index bc6afc8..84ced3b 100644 --- a/drivers/leds/Makefile +++ b/drivers/leds/Makefile @@ -5,6 +5,7 @@ obj-$(CONFIG_LEDS_CLASS) += led-class.o obj-$(CONFIG_LEDS_TRIGGERS) += led-triggers.o # LED Platform Drivers +obj-$(CONFIG_LEDS_ATMEL_PWM) += leds-atmel-pwm.o obj-$(CONFIG_LEDS_CORGI) += leds-corgi.o obj-$(CONFIG_LEDS_LOCOMO) += leds-locomo.o obj-$(CONFIG_LEDS_SPITZ) += leds-spitz.o diff --git a/drivers/leds/leds-atmel-pwm.c b/drivers/leds/leds-atmel-pwm.c new file mode 100644 index 0000000..af61f55 --- /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"); |