On Sat, Oct 1, 2022 at 11:33 AM Eric Chan <e14002...@gmail.com> wrote:
>
> Hi, qemu
>
> As I know, brom will pass 3 parameters to the next stage bootloader, ex:
> openSBI.
> a0 will pass hartid, a2 will pass fw_dynamic_info start address.
> although a1 doesn't use directly in openSBI.
> a1 read value is determined in compile time rather than read from the
> original a1 that passes from brom.
> In qemu/hw/riscv/boot.c
> both 32bit and 64bit machines read 4byte that offset 32byte from the brom
> start address.
>
> for 64 bits machine: a1 read low 32bit data member magic of fw_dynamic_info,
Hello Eric,
a2 will contain the address of the fw_dynamic_info
> the value will same as FW_DYNAMIC_INFO_MAGIC_VALUE because risc-v is little
> endian.
>
> for 32bits machine: each data member of fw_dynamic_info is 4 bytes, so a1
> will read the version rather than magic.
On 32-bit RISC-V a2 will also contain the address of fw_dynamic_info
>
> Do the 32bit and 64bit pass different parameters are expected?
I'm not clear what the difference between the 32-bit and 64-bit
variants are. We use different load instructions, but otherwise they
should be the same functionality.
> If it is not expected, I guess the original version is 64bit machine, and
> then supports 32bit but misses this detail, I hope I can have an opportunity
> to fix this problem.
> If it is expected, why they must be done?
It might be easier to send a patch with any fixes you think should be
made. That way it's easy to understand what you think needs to be
fixed.
Alistair
>
> Thanks,
> Eric Chan
>
> qemu/include/hw/riscv/boot_opensbi.h
> #define FW_DYNAMIC_INFO_MAGIC_VALUE 0x4942534f
> qemu/hw/riscv/boot.c
> void riscv_setup_rom_reset_vec(MachineState *machine, RISCVHartArrayState
> *harts,
> hwaddr start_addr,
> hwaddr rom_base, hwaddr rom_size,
> uint64_t kernel_entry,
> uint64_t fdt_load_addr)
> {
> int i;
> uint32_t start_addr_hi32 = 0x00000000;
> uint32_t fdt_load_addr_hi32 = 0x00000000;
>
> if (!riscv_is_32bit(harts)) {
> start_addr_hi32 = start_addr >> 32;
> fdt_load_addr_hi32 = fdt_load_addr >> 32;
> }
> /* reset vector */
> uint32_t reset_vec[10] = {
> 0x00000297, /* 1: auipc t0, %pcrel_hi(fw_dyn) */
> 0x02828613, /* addi a2, t0, %pcrel_lo(1b) */
> 0xf1402573, /* csrr a0, mhartid */
> 0,
> 0,
> 0x00028067, /* jr t0 */
> start_addr, /* start: .dword */
> start_addr_hi32,
> fdt_load_addr, /* fdt_laddr: .dword */
> fdt_load_addr_hi32,
> /* fw_dyn: */
> };
> if (riscv_is_32bit(harts)) {
> reset_vec[3] = 0x0202a583; /* lw a1, 32(t0) */
> reset_vec[4] = 0x0182a283; /* lw t0, 24(t0) */
> } else {
> reset_vec[3] = 0x0202b583; /* ld a1, 32(t0) */
> reset_vec[4] = 0x0182b283; /* ld t0, 24(t0) */
> }
>
> /* copy in the reset vector in little_endian byte order */
> for (i = 0; i < ARRAY_SIZE(reset_vec); i++) {
> reset_vec[i] = cpu_to_le32(reset_vec[i]);
> }
> rom_add_blob_fixed_as("mrom.reset", reset_vec, sizeof(reset_vec),
> rom_base, &address_space_memory);
> riscv_rom_copy_firmware_info(machine, rom_base, rom_size,
> sizeof(reset_vec),
> kernel_entry);
> }
>
> opensbi/firmware/fw_dynamic.S
> fw_boot_hart:
> /* Sanity checks */
> li a1, FW_DYNAMIC_INFO_MAGIC_VALUE
> REG_L a0, FW_DYNAMIC_INFO_MAGIC_OFFSET(a2)
> bne a0, a1, _bad_dynamic_info
> li a1, FW_DYNAMIC_INFO_VERSION_MAX
> REG_L a0, FW_DYNAMIC_INFO_VERSION_OFFSET(a2)
> bgt a0, a1, _bad_dynamic_info
>
> /* Read boot HART id */
> li a1, FW_DYNAMIC_INFO_VERSION_2
> blt a0, a1, 2f
> REG_L a0, FW_DYNAMIC_INFO_BOOT_HART_OFFSET(a2)
> ret
> 2: li a0, -1
> ret
