[MIPS] 64-bit Sibyte kernels need DMA32.

Sibyte SOCs only have 32-bit PCI.  Due to the sparse use of the address
space only the first 1GB of memory is mapped at physical addresses
below 1GB.  If a system has more than 1GB of memory 32-bit DMA will
not be able to reach all of it.

For now this patch is good enough to keep Sibyte users happy but it seems
eventually something like swiotlb will be needed for Sibyte.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/setup.c

@@ -269,7 +269,7 @@ static void __init bootmem_init(void)
 
 static void __init bootmem_init(void)
 {
-	unsigned long reserved_end;
+	unsigned long init_begin, reserved_end;
 	unsigned long mapstart = ~0UL;
 	unsigned long bootmap_size;
 	int i;
@@ -342,6 +342,35 @@ static void __init bootmem_init(void)
 	 */
 	bootmap_size = init_bootmem_node(NODE_DATA(0), mapstart,
 					 min_low_pfn, max_low_pfn);
+
+
+	init_begin = PFN_UP(__pa_symbol(&__init_begin));
+	for (i = 0; i < boot_mem_map.nr_map; i++) {
+		unsigned long start, end;
+
+		start = PFN_UP(boot_mem_map.map[i].addr);
+		end = PFN_DOWN(boot_mem_map.map[i].addr
+				+ boot_mem_map.map[i].size);
+
+		if (start <= init_begin)
+			start = init_begin;
+		if (start >= end)
+			continue;
+
+#ifndef CONFIG_HIGHMEM
+		if (end > max_low_pfn)
+			end = max_low_pfn;
+
+		/*
+		 * ... finally, is the area going away?
+		 */
+		if (end <= start)
+			continue;
+#endif
+
+		add_active_range(0, start, end);
+	}
+
 	/*
 	 * Register fully available low RAM pages with the bootmem allocator.
 	 */