Dear Igor,
Thank you for your help. However, I took your advice and change to 4.19.35.
I download the source, and replace lpddr4_timing.c which is generated by ddr tool. I also change the imx8mq_evk.h file for the total size of DRAM to 1GB. However, it become worse that the u-boot fail to train the DRAM PHY.
I attached the ddr tool log and u-boot log, please help.
BR
KY