chromeec: Add event methods for EC requested throttle

Two new events possible from the EC for starting and stopping throttle.

These are handled in a per-board method that is defined under the
thermal zone.  This is not quite where I wanted it but the scoping
rules in ACPI don't let me have a defined external object in the
same scope.

Change-Id: I766f07b4365b29df3daa8e45e88f7c38c645c287
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/63988
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/4415
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/ec/google/chromeec/acpi/ec.asl

@@ -23,6 +23,9 @@
  * re-evaluate their _PPC and _CST tables.
  */
 
+// Mainboard specific throttle handler
+External (\_TZ.THRT, MethodObj)
+
 Device (EC0)
 {
 	Name (_HID, EISAID ("PNP0C09"))
@@ -226,6 +229,24 @@ Device (EC0)
 		Store ("EC: KEY PRESSED", Debug)
 	}
 
+	// Throttle Start
+	Method (_Q12, 0, NotSerialized)
+	{
+		Store ("EC: THROTTLE START", Debug)
+		If (CondRefOf (\_TZ.THRT, Local0)) {
+			\_TZ.THRT (1)
+		}
+	}
+
+	// Throttle Stop
+	Method (_Q13, 0, NotSerialized)
+	{
+		Store ("EC: THROTTLE STOP", Debug)
+		If (CondRefOf (\_TZ.THRT, Local0)) {
+			\_TZ.THRT (0)
+		}
+	}
+
 	#include "ac.asl"
 	#include "battery.asl"
 }

src/ec/google/chromeec/ec_commands.h

@@ -239,6 +239,11 @@ enum host_event_code {
 	/* Shutdown due to battery level too low */
 	EC_HOST_EVENT_BATTERY_SHUTDOWN = 17,
 
+        /* Suggest that the AP throttle itself */
+        EC_HOST_EVENT_THROTTLE_START = 18,
+        /* Suggest that the AP resume normal speed */
+        EC_HOST_EVENT_THROTTLE_STOP = 19,
+
 	/*
 	 * The high bit of the event mask is not used as a host event code.  If
 	 * it reads back as set, then the entire event mask should be