+ *
+ * The i.MX28 and i.MX6 types have another field in the MSCR (aka
+ * MII_SPEED) register that defines the MDIO output hold time. Earlier
+ * versions are RAZ there, so just ignore the difference and write the
+ * register always.
+ * The minimal hold time according to IEE802.3 (clause 22) is 10 ns.
+ * HOLDTIME + 1 is the number of clk cycles the fec is holding the
+ * output.
+ * The HOLDTIME bitfield takes values between 0 and 7 (inclusive).
+ * Given that ceil(clkrate / 5000000) <= 64, the calculation for
+ * holdtime cannot result in a value greater than 3.