arch/x86: Add function to determine if we're currently running from CAR

This patch adds a simple function that can be used to check if
CAR_GLOBALs are currently being read from CAR or from DRAM.

Change-Id: Ib7ad0896a691ef6e89e622b985417fedc43579c1
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/19787
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>

src/arch/x86/include/arch/early_variables.h

@@ -44,12 +44,20 @@ static inline void *car_sync_var_ptr(void *var)
 {
 	return var;
 }
+
+static inline int car_active(void)
+{
+	return 1;
+}
 #else
 /* Get the correct pointer for the CAR global variable. */
 void *car_get_var_ptr(void *var);
 
 /* Get and update a CAR_GLOBAL pointing elsewhere in car.global_data*/
 void *car_sync_var_ptr(void *var);
+
+/* Return 1 when currently running with globals in Cache-as-RAM, 0 otherwise. */
+int car_active(void);
 #endif /* ENV_VERSTAGE */
 
 /* Get and set a primitive type global variable. */
@@ -73,6 +81,7 @@ static inline size_t car_object_offset(void *ptr)
 #else
 #define CAR_GLOBAL
 static inline void *car_get_var_ptr(void *var) { return var; }
+static inline int car_active(void) { return 0; }
 #define car_get_var(var) (var)
 #define car_sync_var(var) (var)
 #define car_set_var(var, val)	(var) = (val)

src/cpu/x86/car.c

@@ -113,6 +113,11 @@ void *car_sync_var_ptr(void *var)
 	return mig_var;
 }
 
+int car_active(void)
+{
+	return !car_migrated;
+}
+
 static void do_car_migrate_variables(void)
 {
 	void *migrated_base;