@JeffZhou, it's worth noting that the stock OpenWrt DTS available from Onion does have it set to 40MHz , probably for this exact reason, so it's not a problem for normal builds from the Onion repository. Only when you start to push the boundaries does the issue become apparent. The flash chip itself is rated to 120MHz (I think) so you'll forgive my temptation to try and run it harder rather than settle for 1/3rd of the rated speed