PXA255 MSCx[2:0] setting?

I saw the MSC0_VAL in PXA255 initial code & tried to found how to calculate the best setting for PXA255 with Intel P30 Flash, Yamaha YGV628.
The RDFx, RDNx, RRRx registers are difficult to understand why the value of them came from.

For P30 Flash:
I found the Application Note 768 (Intel Strata Flash Memory(J3) to Intel PXA270 Applications Processor Design Guide). This document mentions the RDFx, RDNx, RRRx came from Intel PXA270 clock speed & flash read/write timing. So, that's it.