driver/ddr/fsl: Fix MRC_CYC calculation for DDR3

For DDR controller version 4.7 or newer, MRC_CYC (mode register set
cycle time) is max(tMRD, tMOD). tMRD is 4nCK, or 8nCK (RDIMM). tMOD
is max(12nCK, 15ns) according to JEDEC spec.

DDR4 is not affected by this change.

Signed-off-by: York Sun <yorksun@freescale.com>

drivers/ddr/fsl/ctrl_regs.c

@@ -324,6 +324,7 @@ static void set_timing_cfg_0(fsl_ddr_cfg_regs_t *ddr,
 #elif defined(CONFIG_SYS_FSL_DDR3)
 	unsigned int data_rate = get_ddr_freq(0);
 	int txp;
+	unsigned int ip_rev;
 	int odt_overlap;
 	/*
 	 * (tXARD and tXARDS). Empirical?
@@ -336,7 +337,25 @@ static void set_timing_cfg_0(fsl_ddr_cfg_regs_t *ddr,
 	 */
 	txp = max((int)mclk_ps * 3, (mclk_ps > 1540 ? 7500 : 6000));
 
-	tmrd_mclk = 4;
+	ip_rev = fsl_ddr_get_version();
+	if (ip_rev >= 0x40700) {
+		/*
+		 * MRS_CYC = max(tMRD, tMOD)
+		 * tMRD = 4nCK (8nCK for RDIMM)
+		 * tMOD = max(12nCK, 15ns)
+		 */
+		tmrd_mclk = max((unsigned int)12, picos_to_mclk(15000));
+	} else {
+		/*
+		 * MRS_CYC = tMRD
+		 * tMRD = 4nCK (8nCK for RDIMM)
+		 */
+		if (popts->registered_dimm_en)
+			tmrd_mclk = 8;
+		else
+			tmrd_mclk = 4;
+	}
+
 	/* set the turnaround time */
 
 	/*