When I compile the kernel, this is the value of CONFIG_CMDLINE in .config

CONFIG_CMDLINE="mem=64M console=ttyS0,115200 initrd=0x21100000,3145728 root=/dev/mtdblock1 rw"

When I boot the board in U-boot, this is bootargs, as seen from printenv:

bootargs=console=ttyS0,115200 root=/dev/mtdblock1 mtdparts=at91_nand:128k(bootst
rap)ro,256k(uboot)ro,128k(env1)ro,128k(env2)ro,2M(linux),-(root) rw rootfstype=j
ffs2

Do these need to match better? The kernel doesn't boot, it just hangs at

Uncompressing Kernel Image ... OK
Starting kernel ...

CONFIG_CMDLINE from kernel config is only used if no other bootargs are specified.
Your U-Boot bootargs are those with which the kernel is started.
But you need to change it a bit. The current setting tries to use the U-Boot binary are as root file system.
Change root=/dev/mtdblock1 to root=/dev/mtdblock5

[quote="Cyberian"]But you need to change it a bit. The current setting tries to use the U-Boot binary are as root file system.
Change root=/dev/mtdblock1 to root=/dev/mtdblock5[/quote]

Interesting...it used to be /dev/mtdblock5 and I had to switch it to /dev/mtdblock1 in order to get things working with the pre-built binaries. But that might be another issue. For now, I switched it to /dev/mtdblock5 but I am still stuck at "Starting kernel..."

EDIT: Even after building with BuildRoot, I still had to change it to /dev/mtdblock1.