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>

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>
David Brownell · Linus Torvalds
1 parent 9a1e8eb1f0
Showing 3 changed files with 165 additions and 0 deletions Side-by-side Diff
drivers/leds/Kconfig
drivers/leds/Makefile
drivers/leds/leds-atmel-pwm.c
@@ -18,6 +18,13 @@
  
 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
@@ -5,6 +5,7 @@
 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
+#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");
...	...	@@ -18,6 +18,13 @@
18	18
19	19	comment "LED drivers"
20	20
	21	+config LEDS_ATMEL_PWM
	22	+ tristate "LED Support using Atmel PWM outputs"
	23	+ depends on LEDS_CLASS && ATMEL_PWM
	24	+ help
	25	+ This option enables support for LEDs driven using outputs
	26	+ of the dedicated PWM controller found on newer Atmel SOCs.
	27	+
21	28	config LEDS_CORGI
22	29	tristate "LED Support for the Sharp SL-C7x0 series"
23	30	depends on LEDS_CLASS && PXA_SHARP_C7xx
...	...	@@ -5,6 +5,7 @@
5	5	obj-$(CONFIG_LEDS_TRIGGERS) += led-triggers.o
6	6
7	7	# LED Platform Drivers
	8	+obj-$(CONFIG_LEDS_ATMEL_PWM) += leds-atmel-pwm.o
8	9	obj-$(CONFIG_LEDS_CORGI) += leds-corgi.o
9	10	obj-$(CONFIG_LEDS_LOCOMO) += leds-locomo.o
10	11	obj-$(CONFIG_LEDS_SPITZ) += leds-spitz.o
	1	+#include <linux/kernel.h>
	2	+#include <linux/platform_device.h>
	3	+#include <linux/leds.h>
	4	+#include <linux/io.h>
	5	+#include <linux/atmel_pwm.h>
	6	+
	7	+
	8	+struct pwmled {
	9	+ struct led_classdev cdev;
	10	+ struct pwm_channel pwmc;
	11	+ struct gpio_led *desc;
	12	+ u32 mult;
	13	+ u8 active_low;
	14	+};
	15	+
	16	+
	17	+/*
	18	+ * For simplicity, we use "brightness" as if it were a linear function
	19	+ * of PWM duty cycle. However, a logarithmic function of duty cycle is
	20	+ * probably a better match for perceived brightness: two is half as bright
	21	+ * as four, four is half as bright as eight, etc
	22	+ */
	23	+static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b)
	24	+{
	25	+ struct pwmled *led;
	26	+
	27	+ /* update the duty cycle for the next period */
	28	+ led = container_of(cdev, struct pwmled, cdev);
	29	+ pwm_channel_writel(&led->pwmc, PWM_CUPD, led->mult * (unsigned) b);
	30	+}
	31	+
	32	+/*
	33	+ * NOTE: we reuse the platform_data structure of GPIO leds,
	34	+ * but repurpose its "gpio" number as a PWM channel number.
	35	+ */
	36	+static int __init pwmled_probe(struct platform_device *pdev)
	37	+{
	38	+ const struct gpio_led_platform_data *pdata;
	39	+ struct pwmled *leds;
	40	+ unsigned i;
	41	+ int status;
	42	+
	43	+ pdata = pdev->dev.platform_data;
	44	+ if (!pdata \|\| pdata->num_leds < 1)
	45	+ return -ENODEV;
	46	+
	47	+ leds = kcalloc(pdata->num_leds, sizeof(*leds), GFP_KERNEL);
	48	+ if (!leds)
	49	+ return -ENOMEM;
	50	+
	51	+ for (i = 0; i < pdata->num_leds; i++) {
	52	+ struct pwmled *led = leds + i;
	53	+ const struct gpio_led *dat = pdata->leds + i;
	54	+ u32 tmp;
	55	+
	56	+ led->cdev.name = dat->name;
	57	+ led->cdev.brightness = LED_OFF;
	58	+ led->cdev.brightness_set = pwmled_brightness;
	59	+ led->cdev.default_trigger = dat->default_trigger;
	60	+
	61	+ led->active_low = dat->active_low;
	62	+
	63	+ status = pwm_channel_alloc(dat->gpio, &led->pwmc);
	64	+ if (status < 0)
	65	+ goto err;
	66	+
	67	+ /*
	68	+ * Prescale clock by 2^x, so PWM counts in low MHz.
	69	+ * Start each cycle with the LED active, so increasing
	70	+ * the duty cycle gives us more time on (== brighter).
	71	+ */
	72	+ tmp = 5;
	73	+ if (!led->active_low)
	74	+ tmp \|= PWM_CPR_CPOL;
	75	+ pwm_channel_writel(&led->pwmc, PWM_CMR, tmp);
	76	+
	77	+ /*
	78	+ * Pick a period so PWM cycles at 100+ Hz; and a multiplier
	79	+ * for scaling duty cycle: brightness * mult.
	80	+ */
	81	+ tmp = (led->pwmc.mck / (1 << 5)) / 100;
	82	+ tmp /= 255;
	83	+ led->mult = tmp;
	84	+ pwm_channel_writel(&led->pwmc, PWM_CDTY,
	85	+ led->cdev.brightness * 255);
	86	+ pwm_channel_writel(&led->pwmc, PWM_CPRD,
	87	+ LED_FULL * tmp);
	88	+
	89	+ pwm_channel_enable(&led->pwmc);
	90	+
	91	+ /* Hand it over to the LED framework */
	92	+ status = led_classdev_register(&pdev->dev, &led->cdev);
	93	+ if (status < 0) {
	94	+ pwm_channel_free(&led->pwmc);
	95	+ goto err;
	96	+ }
	97	+ }
	98	+
	99	+ platform_set_drvdata(pdev, leds);
	100	+ return 0;
	101	+
	102	+err:
	103	+ if (i > 0) {
	104	+ for (i = i - 1; i >= 0; i--) {
	105	+ led_classdev_unregister(&leds[i].cdev);
	106	+ pwm_channel_free(&leds[i].pwmc);
	107	+ }
	108	+ }
	109	+ kfree(leds);
	110	+
	111	+ return status;
	112	+}
	113	+
	114	+static int __exit pwmled_remove(struct platform_device *pdev)
	115	+{
	116	+ const struct gpio_led_platform_data *pdata;
	117	+ struct pwmled *leds;
	118	+ unsigned i;
	119	+
	120	+ pdata = pdev->dev.platform_data;
	121	+ leds = platform_get_drvdata(pdev);
	122	+
	123	+ for (i = 0; i < pdata->num_leds; i++) {
	124	+ struct pwmled *led = leds + i;
	125	+
	126	+ led_classdev_unregister(&led->cdev);
	127	+ pwm_channel_free(&led->pwmc);
	128	+ }
	129	+
	130	+ kfree(leds);
	131	+ platform_set_drvdata(pdev, NULL);
	132	+ return 0;
	133	+}
	134	+
	135	+static struct platform_driver pwmled_driver = {
	136	+ .driver = {
	137	+ .name = "leds-atmel-pwm",
	138	+ .owner = THIS_MODULE,
	139	+ },
	140	+ /* REVISIT add suspend() and resume() methods */
	141	+ .remove = __exit_p(pwmled_remove),
	142	+};
	143	+
	144	+static int __init modinit(void)
	145	+{
	146	+ return platform_driver_probe(&pwmled_driver, pwmled_probe);
	147	+}
	148	+module_init(modinit);
	149	+
	150	+static void __exit modexit(void)
	151	+{
	152	+ platform_driver_unregister(&pwmled_driver);
	153	+}
	154	+module_exit(modexit);
	155	+
	156	+MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness");
	157	+MODULE_LICENSE("GPL");