riscv: Register System RAM as iomem resources

Add System RAM to /proc/iomem, various tools expect it such as kdump.
It is also needed for page_is_ram API which checks the specified address
whether registered as System RAM in iomem_resource list.
Signed-off-by: Zong Li <zong.li@sifive.com>
[Palmer: check MEMBLOCK_NOMAP]
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/mm/init.c

@@ -517,6 +517,32 @@ void mark_rodata_ro(void)
 }
 #endif
 
+void __init resource_init(void)
+{
+	struct memblock_region *region;
+
+	for_each_memblock(memory, region) {
+		struct resource *res;
+
+		res = memblock_alloc(sizeof(struct resource), SMP_CACHE_BYTES);
+		if (!res)
+			panic("%s: Failed to allocate %zu bytes\n", __func__,
+			      sizeof(struct resource));
+
+		if (memblock_is_nomap(region)) {
+			res->name = "reserved";
+			res->flags = IORESOURCE_MEM;
+		} else {
+			res->name = "System RAM";
+			res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
+		}
+		res->start = __pfn_to_phys(memblock_region_memory_base_pfn(region));
+		res->end = __pfn_to_phys(memblock_region_memory_end_pfn(region)) - 1;
+
+		request_resource(&iomem_resource, res);
+	}
+}
+
 void __init paging_init(void)
 {
 	setup_vm_final();
@@ -524,6 +550,7 @@ void __init paging_init(void)
 	sparse_init();
 	setup_zero_page();
 	zone_sizes_init();
+	resource_init();
 }
 
 #ifdef CONFIG_SPARSEMEM_VMEMMAP