DM8148 NAND ECC: uncorrectable error

Hi,

While the 1st stage bootloader is reading the u-boot, I see following message,

NAND read: device 0 offset 0x20000, size 0x40000
ECC: uncorrectable.
NAND read from offset 20000 failed -74
 262144 bytes read: ERROR

But even after error how does the u-boot really come up ?

Thanks & Regards,

MIke