[PATCH] ppc64: fix some issues with mem_reserve

I found a couple of issues with reserve_mem:

- If we try and mem_reserve something of zero length, everything
  reserved after it would get ignored. This is because early_reserve_mem
  sees a zero length as a terminator.
- The code rounded the top down instead of up.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ppc64/kernel/prom_init.c

@@ -587,17 +587,19 @@ static unsigned long __init prom_next_cell(int s, cell_t **cellp)
 static void reserve_mem(unsigned long base, unsigned long size)
 {
 	unsigned long offset = reloc_offset();
-	unsigned long top = base + size;
 	unsigned long cnt = RELOC(mem_reserve_cnt);
 
-	/* We need to always keep one empty entry so that we
+	if (!size)
+		return;
+
+	base = _ALIGN_DOWN(base, PAGE_SIZE);
+	size = _ALIGN_UP(size, PAGE_SIZE);
+
+	/*
+	 * We need to always keep one empty entry so that we
 	 * have our terminator with "size" set to 0 since we are
 	 * dumb and just copy this entire array to the boot params
 	 */
-	base = _ALIGN_DOWN(base, PAGE_SIZE);
-	top = _ALIGN_DOWN(top, PAGE_SIZE);
-	size = top - base;
-
 	if (cnt >= (MEM_RESERVE_MAP_SIZE - 1))
 		prom_panic("Memory reserve map exhausted !\n");
 	RELOC(mem_reserve_map)[cnt].base = base;