Hello Jyotisankar Panda,
This is because P2020DS is not included in SDK 1.8 u-boot source code at all, in the folders configs, include/configs/ and board/freescale/, there are no P2020DS supporting.
Actually P2020DS has already been removed since SDK 1.2 release.
If it is necessary for you to use SDK 1.8, you have to do the porting by yourself according P2020DS source code provided previously.
If you are doing target board bringing up, you also could refer to P2020RDB, which is supported in SDK 1.8.
Previously other customers asked similar questions, you could refer to Problem booting P2020DS with SDK 1.6 images.
Have a great day,
Yiping
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