led: Implement software led blinking

If hardware (or driver) doesn't support leds blinking, it's
now possible to use software implementation of blinking instead.
This relies on cyclic functions.

Signed-off-by: Michael Polyntsov <michael.polyntsov@iopsys.eu>
Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/led/Kconfig b/drivers/led/Kconfig
index 9837960..bee74b2 100644
--- a/drivers/led/Kconfig
+++ b/drivers/led/Kconfig
@@ -65,7 +65,7 @@
 	  Linux compatible ofdata.
 
 config LED_BLINK
-	bool "Support LED blinking"
+	bool "Support hardware LED blinking"
 	depends on LED
 	help
 	  Some drivers can support automatic blinking of LEDs with a given
@@ -73,6 +73,20 @@
 	  This option enables support for this which adds slightly to the
 	  code size.
 
+config LED_SW_BLINK
+	bool "Support software LED blinking"
+	depends on LED
+	select CYCLIC
+	help
+	  Turns on led blinking implemented in the software, useful when
+	  the hardware doesn't support led blinking. Half of the period
+	  led will be ON and the rest time it will be OFF. Standard
+	  led commands can be used to configure blinking. Does nothing
+	  if driver supports hardware blinking.
+	  WARNING: Blinking may be inaccurate during execution of time
+	  consuming commands (ex. flash reading). Also it completely
+	  stops during OS booting.
+
 config SPL_LED
 	bool "Enable LED support in SPL"
 	depends on SPL_DM