iMX8MP + DDR4启动，SPL无法从所有启动设备启动的原因？

U-Boot SPL 2021.04-lf_v2021.04+gd1528947bd (Sep 06 2021 - 08:48:23 +0000)
pca9450_bind: 'pca9450@25' - found regulators subnode
pmic_bind_children for 'pca9450@25' at node offset: 5064
Bound: 0 children for PMIC: 'pca9450@25'
pca9450_bind: pca9450@25 - no child found
pmic_reg_write: reg=c, value=29 priv->trans_len:1, ret=0
pmic_reg_write: reg=10, value=59 priv->trans_len:1, ret=0
pmic_reg_write: reg=1e, value=18 priv->trans_len:1, ret=0
pmic_reg_write: reg=8, value=a1 priv->trans_len:1, ret=0
DDRINFO: start DRAM init
DDRINFO: cfg clk
DDRINFO: DRAM rate 3200MTS
DDRINFO: ddrc config start
DDRINFO: ddrc config done
DDRINFO:ddrphy config start
DRAM PHY training for 3200MTS
check ddr_pmu_train_imem code
check ddr_pmu_train_imem code pass
check ddr4_pmu_train_dmem code
check ddr_pmu_train_dmem code pass
[PMU Major message = 0x00000000]
[PMU Major message = 0x00000002]
[PMU Major message = 0x00000001]
[PMU Major message = 0x0000000a]
[PMU Major message = 0x000000fd]
[PMU Major message = 0x000000fe]
[PMU Major message = 0x00000004]
[PMU Major message = 0x00000003]
[PMU Major message = 0x00000009]
[PMU Major message = 0x00000007]
Training PASS
DRAM PHY training for 3200MTS
check ddr_pmu_train_imem code
check ddr_pmu_train_imem code pass
check ddr4_pmu_train_dmem code
check ddr_pmu_train_dmem code pass
[PMU Major message = 0x00000000]
[PMU Major message = 0x00000006]
[PMU Major message = 0x00000005]
[PMU Major message = 0x00000007]
Training PASS
DDRINFO: ddrphy config done
DDRINFO:ddrphy calibration done
DDRINFO: ddrmix config done
SEC0:  RNG instantiated
Normal Boot
WDT:   Not found!
Trying to boot from BOOTROM
image offset 0x8000, pagesize 0x200, ivt offset 0x0
Can't support legacy image
SPL: failed to boot from all boot devices
### ERROR ### Please RESET the board ###
与 EVK 上的运行图像相比，似乎找不到 BL31 图像：

U-Boot SPL 2021.04-lf_v2021.04+g1c0116f3da (Sep 06 2021 - 08:48:23 +0000)
DDRINFO: start DRAM init
DDRINFO: DRAM rate 4000MTS
DDRINFO:ddrphy calibration done
DDRINFO: ddrmix config done
SEC0:  RNG instantiated
Normal Boot
WDT:   Not found!
Trying to boot from BOOTROM
image offset 0x8000, pagesize 0x200, ivt offset 0x0
NOTICE:  BL31: v2.4(release):lf-5.10.52-2.1.0-rc1-39-gbb4957067
NOTICE:  BL31: Built : 04:45:39, Sep  8 2021


U-Boot 2021.04-lf_v2021.04+g1c0116f3da (Sep 06 2021 - 08:48:23 +0000)

CPU:   i.MX8MP[8] rev1.0 1800 MHz (running at 1200 MHz)
CPU:   Commercial temperature grade (0C to 95C) at 30C
Reset cause: POR
Model: NXP i.MX8MPlus LPDDR4 EVK board
DRAM:  6 GiB
知道我们的定制设计中没有eMMC，只有 micro SD 卡可用，类似于 8MPLUSDR4-CPU 设计。
你能帮助指导我们走得更远吗？