[U-Boot] bootargs

I am booting a linux kernel with U-Boot 2017.11. I want to pass a boot argument "root=/dev/mmcblk1p2". I tried

setenv root /... OR setenv bootargs root=/... saveenv boot

But it still boots with root=/dev/mmcblk0p2 $ cat /proc/cmdline: ... root=/dev/mmcblk0p2 ...

How do I get it to boot with my custom kernel argument?

[the actual problem I am trying to solve this way is "Gave up waiting for root device" when the kernel tries to mount a root fs]

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