intel/car/cache_as_ram_ht.inc: Prepare for dynamic CONFIG_RAMTOP

Change-Id: Idb0f621553e76e771a5d6f2d492675ccd989d947
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/15228
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/cpu/intel/car/cache_as_ram_ht.inc b/src/cpu/intel/car/cache_as_ram_ht.inc
index ee4a1bb..f5256ad 100644
--- a/src/cpu/intel/car/cache_as_ram_ht.inc
+++ b/src/cpu/intel/car/cache_as_ram_ht.inc
@@ -339,8 +339,12 @@
 	post_code(0x2f)
 
 	/* Call romstage.c main function. */
-	call	main
-	addl	$4, %esp
+	call	romstage_main
+
+	/* Save return value from romstage_main. It contains the stack to use
+	 * after cache-as-ram is torn down. It also contains the information
+	 * for setting up MTRRs. */
+	movl	%eax, %ebx
 
 	post_code(0x30)
 
@@ -425,7 +429,8 @@
 	post_code(POST_PREPARE_RAMSTAGE)
 	cld			/* Clear direction flag. */
 
-	movl	$CONFIG_RAMTOP, %esp
+	/* Setup stack as indicated by return value from romstage_main(). */
+	movl	%ebx, %esp
 	movl	%esp, %ebp
 	call	copy_and_run