extpower: Allow board to override signal debounce time

This is for boards on which AC_PRESENT can be expected to fluctuate
over a much longer period than the code was originally designed for.
Specifically, USB-PD systems may require several hundred milliseconds
for the state machine to settle before making decisions based on
AC_PRESENT status, for example, changing LED state.

BUG=chrome-os-partner:56471
BRANCH=none
TEST=Tested on Reef with follow-up patch

Change-Id: I370048cb79d1593a14077563ec8db8e8282afb16
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/378755

common/extpower_gpio.c

@@ -12,8 +12,6 @@
 #include "host_command.h"
 #include "timer.h"
 
-#define EXTPOWER_DEBOUNCE_US  (30 * MSEC)
-
 static int debounced_extpower_presence;
 
 int extpower_is_present(void)
@@ -45,7 +43,8 @@ DECLARE_DEFERRED(extpower_deferred);
 void extpower_interrupt(enum gpio_signal signal)
 {
 	/* Trigger deferred notification of external power change */
-	hook_call_deferred(&extpower_deferred_data, EXTPOWER_DEBOUNCE_US);
+	hook_call_deferred(&extpower_deferred_data,
+			CONFIG_EXTPOWER_DEBOUNCE_MS * MSEC);
 }
 
 static void extpower_init(void)

include/config.h

@@ -812,6 +812,9 @@
 /* Support detecting external power presence via a GPIO */
 #undef CONFIG_EXTPOWER_GPIO
 
+/* Default debounce time for external power signal */
+#define CONFIG_EXTPOWER_DEBOUNCE_MS 30
+
 /*****************************************************************************/
 /* Number of cooling fans. Undef if none. */
 #undef CONFIG_FANS