Re: [PATCH v2 for-8.2] ppc/amigaone: Allow running AmigaOS without firmware image

["Nicholas Piggin" <npiggin@gmail.com>]

On Sun Nov 26, 2023 at 2:34 AM AEST, BALATON Zoltan wrote:
> The machine uses a modified U-Boot under GPL license but the sources
> of it are lost with only a binary available so it cannot be included
> in QEMU. Allow running without the firmware image with -bios none
> which can be used when calling a boot loader directly and thus
> simplifying booting guests. We need a small routine that AmigaOS calls
> from ROM which is added in this case to allow booting AmigaOS without
> external firmware image.
>
> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
> ---
> v2: Unfortunately AmigaOS needs some additional ROM part which is added
> Please merge for 8.2 as it allows booting AmigaOS simpler without
> having to download separate firmware.

How to test this?

>
>  hw/ppc/amigaone.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/hw/ppc/amigaone.c b/hw/ppc/amigaone.c
> index 992a55e632..a11d2d5556 100644
> --- a/hw/ppc/amigaone.c
> +++ b/hw/ppc/amigaone.c
> @@ -40,6 +40,16 @@
>  #define PROM_ADDR 0xfff00000
>  #define PROM_SIZE (512 * KiB)
>  
> +/* AmigaOS calls this routine from ROM, use this if -bios none */
> +static const char dummy_fw[] = {
> +    0x38, 0x00, 0x00, 0x08, /* li      r0,8 */
> +    0x7c, 0x09, 0x03, 0xa6, /* mtctr   r0 */
> +    0x54, 0x63, 0xf8, 0x7e, /* srwi    r3,r3,1 */
> +    0x42, 0x00, 0xff, 0xfc, /* bdnz    0x8 */
> +    0x7c, 0x63, 0x18, 0xf8, /* not     r3,r3 */
> +    0x4e, 0x80, 0x00, 0x20, /* blr */
> +};

This is clever, but does anything else create blobs like this?
It could be put into a .S in pc-bios, which might be a bit more
consistent.

We might make a ppc/ subdirectory under there, but that's for
another time.

Thanks,
Nick

> +
>  static void amigaone_cpu_reset(void *opaque)
>  {
>      PowerPCCPU *cpu = opaque;
> @@ -94,17 +104,21 @@ static void amigaone_init(MachineState *machine)
>      }
>  
>      /* allocate and load firmware */
> +    rom = g_new(MemoryRegion, 1);
> +    memory_region_init_rom(rom, NULL, "rom", PROM_SIZE, &error_fatal);
> +    memory_region_add_subregion(get_system_memory(), PROM_ADDR, rom);
>      filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, fwname);
>      if (filename) {
> -        rom = g_new(MemoryRegion, 1);
> -        memory_region_init_rom(rom, NULL, "rom", PROM_SIZE, &error_fatal);
> -        memory_region_add_subregion(get_system_memory(), PROM_ADDR, rom);
>          sz = load_image_targphys(filename, PROM_ADDR, PROM_SIZE);
>          if (sz <= 0 || sz > PROM_SIZE) {
>              error_report("Could not load firmware '%s'", filename);
>              exit(1);
>          }
>          g_free(filename);
> +    } else if (!strcmp(fwname, "none")) {
> +        address_space_write_rom(&address_space_memory, 0xfff7ff80,
> +                                MEMTXATTRS_UNSPECIFIED, dummy_fw,
> +                                ARRAY_SIZE(dummy_fw));
>      } else if (!qtest_enabled()) {
>          error_report("Could not find firmware '%s'", fwname);
>          exit(1);