x86, mtrr: Refactor MTRR type overlap check code

Move the MTRR type overlap check into a new function. No functional change in
this patch. Just making it easier to add multiple region overlap check in
the following patch.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
LKML-Reference: <1284159350-19841-2-git-send-email-venki@google.com>
Reviewed-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/kernel/cpu/mtrr/generic.c

@@ -64,6 +64,33 @@ static inline void k8_check_syscfg_dram_mod_en(void)
 	}
 }
 
+/*
+ * Check and return the effective type for MTRR-MTRR type overlap.
+ * Returns 1 if the effective type is UNCACHEABLE, else returns 0
+ */
+static int check_type_overlap(u8 *prev, u8 *curr)
+{
+	if (*prev == MTRR_TYPE_UNCACHABLE || *curr == MTRR_TYPE_UNCACHABLE) {
+		*prev = MTRR_TYPE_UNCACHABLE;
+		*curr = MTRR_TYPE_UNCACHABLE;
+		return 1;
+	}
+
+	if ((*prev == MTRR_TYPE_WRBACK && *curr == MTRR_TYPE_WRTHROUGH) ||
+	    (*prev == MTRR_TYPE_WRTHROUGH && *curr == MTRR_TYPE_WRBACK)) {
+		*prev = MTRR_TYPE_WRTHROUGH;
+		*curr = MTRR_TYPE_WRTHROUGH;
+	}
+
+	if (*prev != *curr) {
+		*prev = MTRR_TYPE_UNCACHABLE;
+		*curr = MTRR_TYPE_UNCACHABLE;
+		return 1;
+	}
+
+	return 0;
+}
+
 /*
  * Returns the effective MTRR type for the region
  * Error returns:
@@ -138,21 +165,8 @@ u8 mtrr_type_lookup(u64 start, u64 end)
 			continue;
 		}
 
-		if (prev_match == MTRR_TYPE_UNCACHABLE ||
-		    curr_match == MTRR_TYPE_UNCACHABLE) {
-			return MTRR_TYPE_UNCACHABLE;
-		}
-
-		if ((prev_match == MTRR_TYPE_WRBACK &&
-		     curr_match == MTRR_TYPE_WRTHROUGH) ||
-		    (prev_match == MTRR_TYPE_WRTHROUGH &&
-		     curr_match == MTRR_TYPE_WRBACK)) {
-			prev_match = MTRR_TYPE_WRTHROUGH;
-			curr_match = MTRR_TYPE_WRTHROUGH;
-		}
-
-		if (prev_match != curr_match)
-			return MTRR_TYPE_UNCACHABLE;
+		if (check_type_overlap(&prev_match, &curr_match))
+			return curr_match;
 	}
 
 	if (mtrr_tom2) {