spring: Enable low power mode.

This mode was disabled initially to make sure it didn't side-effect
things during early development.  Now that branch is cut lets
re-enable and backport when stability is proven.

Signed-off-by: Todd Broch <tbroch@chromium.org>

BRANCH=spring
BUG=chrome-os-partner:17587
TEST=manual, install & run on Spring ... system functions.

When device is plugged stays awake regardless of battery state.
When device is unplugged sleeps and power is saved.
When device is re-plugged awakes.

Change-Id: I9a85fa7376d1a94c9864beed3d053e8b49480959
Reviewed-on: https://gerrit.chromium.org/gerrit/45594
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
Commit-Queue: Todd Broch <tbroch@chromium.org>

board/spring/board.h

@@ -26,8 +26,8 @@
 #undef  CONFIG_TASK_PROFILING
 #define CONFIG_WATCHDOG_HELP
 
-/* DE-ACTIVATED: use STOP mode when we have nothing to do */
-#undef CONFIG_LOW_POWER_IDLE
+/* use STOP mode when we have nothing to do */
+#define CONFIG_LOW_POWER_IDLE
 
 /* Smart battery and TPSchrome are on a private I2C bus behind the EC */
 #define CONFIG_I2C_PASSTHROUGH

board/spring/usb_charging.c

@@ -8,6 +8,7 @@
 #include "adc.h"
 #include "board.h"
 #include "chipset.h"
+#include "clock.h"
 #include "console.h"
 #include "hooks.h"
 #include "gpio.h"
@@ -494,6 +495,10 @@ static void usb_device_change(int dev_type)
 	keyboard_send_battery_key();
 
 	current_dev_type = dev_type;
+	if (dev_type)
+		disable_sleep(SLEEP_MASK_USB_PWR);
+	else
+		enable_sleep(SLEEP_MASK_USB_PWR);
 }
 
 /*

include/clock.h

@@ -46,6 +46,7 @@ enum {
 	SLEEP_MASK_UART   = (1 << 1), /* UART communication on-going */
 	SLEEP_MASK_I2C    = (1 << 2), /* I2C master communication on-going */
 	SLEEP_MASK_CHARGING = (1 << 3), /* Charging loop on-going */
+	SLEEP_MASK_USB_PWR = (1 << 4), /* USB power loop on-going */
 
 	SLEEP_MASK_FORCE  = (1 << 31), /* Force disabling low power modes */
 };