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, 7 insertions, 0 deletions

diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index 851a3b01781..859814f62cb 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