hw/loongarch: Load FDT table into dram memory space

Load FDT table into dram memory space, and the addr is 2 MiB.
Since lowmem region starts from 0, FDT base address is located
at 2 MiB to avoid NULL pointer access.

Signed-off-by: Xiaojuan Yang <yangxiaojuan@loongson.cn>
Acked-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20221028014007.2718352-2-yangxiaojuan@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>

hw/loongarch/virt.c

@@ -159,7 +159,6 @@ static void fdt_add_pcie_node(const LoongArchMachineState *lams)
                                  1, FDT_PCI_RANGE_MMIO, 2, base_mmio,
                                  2, base_mmio, 2, size_mmio);
     g_free(nodename);
-    qemu_fdt_dumpdtb(ms->fdt, lams->fdt_size);
 }
 
 static void fdt_add_irqchip_node(LoongArchMachineState *lams)
@@ -656,6 +655,7 @@ static void loongarch_init(MachineState *machine)
     MemoryRegion *address_space_mem = get_system_memory();
     LoongArchMachineState *lams = LOONGARCH_MACHINE(machine);
     int i;
+    hwaddr fdt_base;
 
     if (!cpu_model) {
         cpu_model = LOONGARCH_CPU_TYPE_NAME("la464");
@@ -760,12 +760,16 @@ static void loongarch_init(MachineState *machine)
     lams->machine_done.notify = virt_machine_done;
     qemu_add_machine_init_done_notifier(&lams->machine_done);
     fdt_add_pcie_node(lams);
-
-    /* load fdt */
-    MemoryRegion *fdt_rom = g_new(MemoryRegion, 1);
-    memory_region_init_rom(fdt_rom, NULL, "fdt", VIRT_FDT_SIZE, &error_fatal);
-    memory_region_add_subregion(get_system_memory(), VIRT_FDT_BASE, fdt_rom);
-    rom_add_blob_fixed("fdt", machine->fdt, lams->fdt_size, VIRT_FDT_BASE);
+    /*
+     * Since lowmem region starts from 0, FDT base address is located
+     * at 2 MiB to avoid NULL pointer access.
+     *
+     * Put the FDT into the memory map as a ROM image: this will ensure
+     * the FDT is copied again upon reset, even if addr points into RAM.
+     */
+    fdt_base = 2 * MiB;
+    qemu_fdt_dumpdtb(machine->fdt, lams->fdt_size);
+    rom_add_blob_fixed("fdt", machine->fdt, lams->fdt_size, fdt_base);
 }
 
 bool loongarch_is_acpi_enabled(LoongArchMachineState *lams)

include/hw/loongarch/virt.h

@@ -28,9 +28,6 @@
 #define VIRT_GED_MEM_ADDR       (VIRT_GED_EVT_ADDR + ACPI_GED_EVT_SEL_LEN)
 #define VIRT_GED_REG_ADDR       (VIRT_GED_MEM_ADDR + MEMORY_HOTPLUG_IO_LEN)
 
-#define VIRT_FDT_BASE           0x1c400000
-#define VIRT_FDT_SIZE           0x100000
-
 struct LoongArchMachineState {
     /*< private >*/
     MachineState parent_obj;