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>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile
index bc6afc8dcb27..84ced3b1a13d 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