spi: spi-cadence-quadspi: Search for rxlow at incrementing TX values

commit 44a68f7b5931677bd0a99cf7d6683ce7ca05331f from
git://git.ti.com/ti-linux-kernel/ti-linux-kernel.git

Sometimes TX = 16 might fall outside the range of valid TX values. In
that case, the tuning algorithm would be unable to find rxlow or rxhigh,
and give up. If TX = 16 is on the border of the valid range, then on
some runs it would succeed and on some others it would fail.

So if rxlow is not found at the initial TX value of 16, do not give up.
Instead, increment the TX and look for it again. This process is
repeated until the TX crosses a threshold, after which an error is
returned. A similar process is followed for the upper TX boundary as
well.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Xulin Sun <xulin.sun@windriver.com>

drivers/spi/spi-cadence-quadspi.c

@@ -277,6 +277,8 @@ struct cqspi_driver_platdata {
 #define CQSPI_PHY_HIGH_RX_BOUND		25
 #define CQSPI_PHY_LOW_TX_BOUND		32
 #define CQSPI_PHY_HIGH_TX_BOUND		48
+#define CQSPI_PHY_TX_LOOKUP_LOW_BOUND	24
+#define CQSPI_PHY_TX_LOOKUP_HIGH_BOUND	38
 
 #define CQSPI_PHY_DEFAULT_TEMP		45
 #define CQSPI_PHY_MIN_TEMP		-45
@@ -575,15 +577,19 @@ static int cqspi_phy_calibrate(struct cqspi_flash_pdata *f_pdata,
 
 	/* Look for RX boundaries at TX = 16. */
 	rxlow.tx = 16;
-	rxhigh.tx = 16;
 
-	rxlow.read_delay = CQSPI_PHY_INIT_RD;
-	ret = cqspi_find_rx_low(f_pdata, mem, &rxlow);
+	do {
+		dev_dbg(dev, "Searching for rxlow on TX = %d\n", rxlow.tx);
+		rxlow.read_delay = CQSPI_PHY_INIT_RD;
+		ret = cqspi_find_rx_low(f_pdata, mem, &rxlow);
+	} while (ret && ++rxlow.tx <= CQSPI_PHY_TX_LOOKUP_LOW_BOUND);
+
 	if (ret)
 		goto out;
 	dev_dbg(dev, "rxlow: RX: %d TX: %d RD: %d\n", rxlow.rx, rxlow.tx,
 		rxlow.read_delay);
 
+	rxhigh.tx = rxlow.tx;
 	rxhigh.read_delay = rxlow.read_delay;
 	cqspi_find_rx_high(f_pdata, mem, &rxhigh);
 	if (ret)
@@ -601,9 +607,14 @@ static int cqspi_phy_calibrate(struct cqspi_flash_pdata *f_pdata,
 
 		/* Look for RX boundaries at TX = 48. */
 		temp.tx = 48;
-		temp.read_delay = CQSPI_PHY_INIT_RD;
 
-		ret = cqspi_find_rx_low(f_pdata, mem, &temp);
+		do {
+			dev_dbg(dev, "Searching for rxlow on TX = %d\n",
+				temp.tx);
+			temp.read_delay = CQSPI_PHY_INIT_RD;
+			ret = cqspi_find_rx_low(f_pdata, mem, &temp);
+		} while (ret && --temp.tx >= CQSPI_PHY_TX_LOOKUP_HIGH_BOUND);
+
 		if (ret)
 			goto out;
 		dev_dbg(dev, "rxlow: RX: %d TX: %d RD: %d\n", temp.rx, temp.tx,