imx8ulp: ddr: Fix DDR frequency request issue

After acking the requested frequency, should wait the ack bit clear
by DDR controller and check the DFS interrupt for next request polling.
Otherwise, the next polling of request bit will get previous value
that DDR controller have not cleared it, so a wrong request frequency
is used.

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>

drivers/ddr/imx/imx8ulp/ddr_init.c

@@ -129,8 +129,8 @@ int ddr_calibration(unsigned int fsp_table[3])
 		 * Polling SIM LPDDR_CTRL2 Bit phy_freq_chg_req until be 1'b1
 		 */
 		reg_val = readl(AVD_SIM_LPDDR_CTRL2);
-		phy_freq_req = (reg_val >> 7) & 0x1;
-
+		/* DFS interrupt is set */
+		phy_freq_req = ((reg_val >> 7) & 0x1) && ((reg_val >> 15) & 0x1);
 		if (phy_freq_req) {
 			phy_freq_type = reg_val & 0x1F;
 			if (phy_freq_type == 0x00) {
@@ -159,7 +159,11 @@ int ddr_calibration(unsigned int fsp_table[3])
 				if (freq_chg_pt == 2)
 					freq_chg_cnt--;
 			}
-			reg_val = readl(AVD_SIM_LPDDR_CTRL2);
+
+			/* Hardware clear the ack on falling edge of LPDDR_CTRL2:phy_freq_chg_reg */
+			/* Ensure the ack is clear before starting to poll request again */
+			while ((readl(AVD_SIM_LPDDR_CTRL2) & BIT(6)))
+				;
 		}
 	} while (1);