[S390] Rework create_mem_hole() function

This patch makes the create_mem_hole() function more readable and
fixes some minor bugs (e.g. off-by-one problems).
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/mem_detect.c

@@ -63,71 +63,83 @@ void detect_memory_layout(struct mem_chunk chunk[])
 }
 EXPORT_SYMBOL(detect_memory_layout);
 
+/*
+ * Move memory chunks array from index "from" to index "to"
+ */
+static void mem_chunk_move(struct mem_chunk chunk[], int to, int from)
+{
+	int cnt = MEMORY_CHUNKS - to;
+
+	memmove(&chunk[to], &chunk[from], cnt * sizeof(struct mem_chunk));
+}
+
+/*
+ * Initialize memory chunk
+ */
+static void mem_chunk_init(struct mem_chunk *chunk, unsigned long addr,
+			   unsigned long size, int type)
+{
+	chunk->type = type;
+	chunk->addr = addr;
+	chunk->size = size;
+}
+
 /*
  * Create memory hole with given address, size, and type
  */
-void create_mem_hole(struct mem_chunk chunks[], unsigned long addr,
+void create_mem_hole(struct mem_chunk chunk[], unsigned long addr,
 		     unsigned long size, int type)
 {
-	unsigned long start, end, new_size;
-	int i;
+	unsigned long lh_start, lh_end, lh_size, ch_start, ch_end, ch_size;
+	int i, ch_type;
 
 	for (i = 0; i < MEMORY_CHUNKS; i++) {
-		if (chunks[i].size == 0)
-			continue;
-		if (addr + size < chunks[i].addr)
-			continue;
-		if (addr >= chunks[i].addr + chunks[i].size)
+		if (chunk[i].size == 0)
 			continue;
-		start = max(addr, chunks[i].addr);
-		end = min(addr + size, chunks[i].addr + chunks[i].size);
-		new_size = end - start;
-		if (new_size == 0)
-			continue;
-		if (start == chunks[i].addr &&
-		    end == chunks[i].addr + chunks[i].size) {
-			/* Remove chunk */
-			chunks[i].type = type;
-		} else if (start == chunks[i].addr) {
-			/* Make chunk smaller at start */
-			if (i >= MEMORY_CHUNKS - 1)
-				panic("Unable to create memory hole");
-			memmove(&chunks[i + 1], &chunks[i],
-				sizeof(struct mem_chunk) *
-				(MEMORY_CHUNKS - (i + 1)));
-			chunks[i + 1].addr = chunks[i].addr + new_size;
-			chunks[i + 1].size = chunks[i].size - new_size;
-			chunks[i].size = new_size;
-			chunks[i].type = type;
-			i += 1;
-		} else if (end == chunks[i].addr + chunks[i].size) {
-			/* Make chunk smaller at end */
-			if (i >= MEMORY_CHUNKS - 1)
-				panic("Unable to create memory hole");
-			memmove(&chunks[i + 1], &chunks[i],
-				sizeof(struct mem_chunk) *
-				(MEMORY_CHUNKS - (i + 1)));
-			chunks[i + 1].addr = start;
-			chunks[i + 1].size = new_size;
-			chunks[i + 1].type = type;
-			chunks[i].size -= new_size;
+
+		/* Define chunk properties */
+		ch_start = chunk[i].addr;
+		ch_size = chunk[i].size;
+		ch_end = ch_start + ch_size - 1;
+		ch_type = chunk[i].type;
+
+		/* Is memory chunk hit by memory hole? */
+		if (addr + size <= ch_start)
+			continue; /* No: memory hole in front of chunk */
+		if (addr > ch_end)
+			continue; /* No: memory hole after chunk */
+
+		/* Yes: Define local hole properties */
+		lh_start = max(addr, chunk[i].addr);
+		lh_end = min(addr + size - 1, ch_end);
+		lh_size = lh_end - lh_start + 1;
+
+		if (lh_start == ch_start && lh_end == ch_end) {
+			/* Hole covers complete memory chunk */
+			mem_chunk_init(&chunk[i], lh_start, lh_size, type);
+		} else if (lh_end == ch_end) {
+			/* Hole starts in memory chunk and convers chunk end */
+			mem_chunk_move(chunk, i + 1, i);
+			mem_chunk_init(&chunk[i], ch_start, ch_size - lh_size,
+				       ch_type);
+			mem_chunk_init(&chunk[i + 1], lh_start, lh_size, type);
 			i += 1;
+		} else if (lh_start == ch_start) {
+			/* Hole ends in memory chunk */
+			mem_chunk_move(chunk, i + 1, i);
+			mem_chunk_init(&chunk[i], lh_start, lh_size, type);
+			mem_chunk_init(&chunk[i + 1], lh_end + 1,
+				       ch_size - lh_size, ch_type);
+			break;
 		} else {
-			/* Create memory hole */
-			if (i >= MEMORY_CHUNKS - 2)
-				panic("Unable to create memory hole");
-			memmove(&chunks[i + 2], &chunks[i],
-				sizeof(struct mem_chunk) *
-				(MEMORY_CHUNKS - (i + 2)));
-			chunks[i + 1].addr = addr;
-			chunks[i + 1].size = size;
-			chunks[i + 1].type = type;
-			chunks[i + 2].addr = addr + size;
-			chunks[i + 2].size =
-				chunks[i].addr + chunks[i].size - (addr + size);
-			chunks[i + 2].type = chunks[i].type;
-			chunks[i].size = addr - chunks[i].addr;
-			i += 2;
+			/* Hole splits memory chunk */
+			mem_chunk_move(chunk, i + 2, i);
+			mem_chunk_init(&chunk[i], ch_start,
+				       lh_start - ch_start, ch_type);
+			mem_chunk_init(&chunk[i + 1], lh_start, lh_size, type);
+			mem_chunk_init(&chunk[i + 2], lh_end + 1,
+				       ch_end - lh_end, ch_type);
+			break;
 		}
 	}
 }