Either: In UBoot, set the environment variable bootargs to include the phrase:
Zero, x, eight, seven zeroes.
Or: In Linux, the kernel L2 driver can be controlled via the interface /proc/sys/kernel/l2cr.
Just read the ascii string from the interface using cat /proc/sys/kernel/l2cr.
If you want to change it, just overwrite the hex value with a new one with:
echo 'hexcode' > /proc/sys/kernel/l2cr.
Enable with hex code 0x80000000, disable with 0x00000000.
OS4 will probably enable this by default.