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>
---
 hw/loongarch/virt.c         | 18 +++++++++++-------
 include/hw/loongarch/virt.h |  3 ---
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/hw/loongarch/virt.c b/hw/loongarch/virt.c
index 29df99727d..fe33e7e3e4 100644
--- a/hw/loongarch/virt.c
+++ b/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)
@@ -689,6 +688,7 @@ 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");
@@ -793,12 +793,16 @@ 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)
diff --git a/include/hw/loongarch/virt.h b/include/hw/loongarch/virt.h
index 09f1c88ee5..45c383f5a7 100644
--- a/include/hw/loongarch/virt.h
+++ b/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;
-- 
2.31.1

在 2022/10/28 上午9:40, Xiaojuan Yang 写道:
> 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>
> ---
>   hw/loongarch/virt.c         | 18 +++++++++++-------
>   include/hw/loongarch/virt.h |  3 ---
>   2 files changed, 11 insertions(+), 10 deletions(-)
Acked-by: Song Gao <gaosong@loongson.cn>

Thanks.
Song Gao
> diff --git a/hw/loongarch/virt.c b/hw/loongarch/virt.c
> index 29df99727d..fe33e7e3e4 100644
> --- a/hw/loongarch/virt.c
> +++ b/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)
> @@ -689,6 +688,7 @@ 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");
> @@ -793,12 +793,16 @@ 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)
> diff --git a/include/hw/loongarch/virt.h b/include/hw/loongarch/virt.h
> index 09f1c88ee5..45c383f5a7 100644
> --- a/include/hw/loongarch/virt.h
> +++ b/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;