coreboot

I got a gizmo2 development board. the official hardware and software support stopped a long time ago and no BIOS source code was released.
I tried to compile coreboot firmware to support some new features. The latest supported coreboot version is 4.18.
I flashed and booted the gizmo2 development board, there is no video output during the coreboot startup phase, but it boots the OS normally and the OS has video output, I purchased a FT232H board for printing logs, and it seems like there are a lot of problems.

FMAP REGION: COREBOOT
Name                           Offset     Type           Size   Comp
cbfs_master_header             0x0        cbfs header        32 none
config                         0x80       raw               562 none
revision                       0x300      raw               720 none
build_info                     0x600      raw               103 none
spd.bin                        0x6c0      spd               128 none
fallback/dsdt.aml              0x780      raw              6172 none
cmos_layout.bin                0x2000     cmos_layout       616 none
fallback/postcar               0x22c0     stage           22312 none
payload_config                 0x7a40     raw              1621 none
payload_revision               0x80c0     raw               237 none
(empty)                        0x8200     null            31652 none
apu/amdfw                      0xfdc0     raw            135168 none
fallback/romstage              0x30e00    stage          387544 none
fallback/ramstage              0x8f880    stage          136240 LZMA (311716 decompressed)
pci1002,9830.rom               0xb0d40    optionrom       59392 none
fallback/payload               0xbf580    simple elf      72695 none
(empty)                        0xd11c0    null          3255268 none
bootblock                      0x3ebdc0   bootblock       16384 none