MIPS: Loongson3,SGI-IP27: Simplify max_low_pfn calculation

Both the Loongson3 & SGI-IP27 platforms set max_low_pfn to the last
available PFN describing memory. They both do it in paging_init() which
is later than ideal since max_low_pfn is used before that function is
called. Simplify both platforms to trivially initialize max_low_pfn
using the end address of DRAM, and do it earlier in prom_meminit().

Signed-off-by: Paul Burton <[e-mail]>
Suggested-by: Mike Rapoport <[e-mail]>
Tested-by: Thomas Bogendoerfer <[e-mail]>
Patchwork: https://patchwork.linux-mips.org/patch/21104/
References: https://patchwork.linux-mips.org/patch/21031/
Cc: Huacai Chen <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Thomas Bogendoerfer <[e-mail]>
Cc: [e-mail]

arch/mips/loongson64/loongson-3/numa.c

···
 			cpumask_clear(&__node_data[(node)]->cpumask);
 		}
 	}
+	max_low_pfn = PHYS_PFN(memblock_end_of_DRAM());
+
 	for (cpu = 0; cpu < loongson_sysconf.nr_cpus; cpu++) {
 		node = cpu / loongson_sysconf.cores_per_node;
 		if (node >= num_online_nodes())
···
 
 void __init paging_init(void)
 {
-	unsigned node;
 	unsigned long zones_size[MAX_NR_ZONES] = {0, };
 
 	pagetable_init();
-
-	for_each_online_node(node) {
-		unsigned long  start_pfn, end_pfn;
-
-		get_pfn_range_for_nid(node, &start_pfn, &end_pfn);
-
-		if (end_pfn > max_low_pfn)
-			max_low_pfn = end_pfn;
-	}
 #ifdef CONFIG_ZONE_DMA32
 	zones_size[ZONE_DMA32] = MAX_DMA32_PFN;
 #endif

arch/mips/sgi-ip27/ip27-memory.c

···
 
 	mlreset();
 	szmem();
+	max_low_pfn = PHYS_PFN(memblock_end_of_DRAM());
 
 	for (node = 0; node < MAX_COMPACT_NODES; node++) {
 		if (node_online(node)) {
···
 void __init paging_init(void)
 {
 	unsigned long zones_size[MAX_NR_ZONES] = {0, };
-	unsigned node;
 
 	pagetable_init();
-
-	for_each_online_node(node) {
-		unsigned long start_pfn, end_pfn;
-
-		get_pfn_range_for_nid(node, &start_pfn, &end_pfn);
-
-		if (end_pfn > max_low_pfn)
-			max_low_pfn = end_pfn;
-	}
 	zones_size[ZONE_NORMAL] = max_low_pfn;
 	free_area_init_nodes(zones_size);
 }