spi: zynqmp_gqspi: fix set_speed bug on multiple runs

If zynqmp_qspi_set_speed() is called multiple times with the same speed,
then on the second call it will skip recalculating the baud_rate_val as
it assumes the speed is already configured correctly. But it will still
write the baud_rate_val to the configuration register and call
zynqmp_gqspi_set_tapdelay(). Because it skipped recalculating the
baud_rate_val, it will use the initial value of 0 . This causes the
driver to run at maximum speed which for many spi flashes is too fast and
causes data corruption.

Instead only write out a new baud_rate_val if we have calculated the
correct baud_rate_val.

This opens up another issue with the "if (speed == 0)", we don't save
off the new plat->speed_hz value when setting the baud rate on the
speed=0 path. Instead mimic what the Linux zynqmp gqspi driver does, and
have speed==0 just use the same calculation as a normal speed. That will
cause the baud_rate_val to use the slowest speed possible, which is the
safest option.
Signed-off-by: NBrandon Maier <brandon.maier@rockwellcollins.com>
CC: jagan@amarulasolutions.com
CC: michal.simek@xilinx.com
CC: Ashok Reddy Soma <ashokred@xilinx.com>
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

drivers/spi/zynqmp_gqspi.c

@@ -320,12 +320,9 @@ static int zynqmp_qspi_set_speed(struct udevice *bus, uint speed)
 	if (speed > plat->frequency)
 		speed = plat->frequency;
 
-	/* Set the clock frequency */
-	confr = readl(&regs->confr);
-	if (speed == 0) {
-		/* Set baudrate x8, if the freq is 0 */
-		baud_rate_val = GQSPI_DFLT_BAUD_RATE_VAL;
-	} else if (plat->speed_hz != speed) {
+	if (plat->speed_hz != speed) {
+		/* Set the clock frequency */
+		/* If speed == 0, default to lowest speed */
 		while ((baud_rate_val < 8) &&
 		       ((plat->frequency /
 		       (2 << baud_rate_val)) > speed))
@@ -335,13 +332,15 @@ static int zynqmp_qspi_set_speed(struct udevice *bus, uint speed)
 			baud_rate_val = GQSPI_DFLT_BAUD_RATE_VAL;
 
 		plat->speed_hz = plat->frequency / (2 << baud_rate_val);
-	}
-	confr &= ~GQSPI_BAUD_DIV_MASK;
-	confr |= (baud_rate_val << 3);
-	writel(confr, &regs->confr);
 
-	zynqmp_qspi_set_tapdelay(bus, baud_rate_val);
-	debug("regs=%p, speed=%d\n", priv->regs, plat->speed_hz);
+		confr = readl(&regs->confr);
+		confr &= ~GQSPI_BAUD_DIV_MASK;
+		confr |= (baud_rate_val << 3);
+		writel(confr, &regs->confr);
+		zynqmp_qspi_set_tapdelay(bus, baud_rate_val);
+
+		debug("regs=%p, speed=%d\n", priv->regs, plat->speed_hz);
+	}
 
 	return 0;
 }