serial: max310x: fail probe if clock crystal is unstable

A stable clock is really required in order to use this UART, so log an
error message and bail out if the chip reports that the clock is not
stable.

Fixes: 4cf9a88 ("serial: max310x: Check the clock readiness")
Cc: stable@vger.kernel.org
Suggested-by: Jan Kundrát <jan.kundrat@cesnet.cz>
Link: https://www.spinics.net/lists/linux-serial/msg35773.html
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20240116213001.3691629-4-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/max310x.c

@@ -587,7 +587,7 @@ static int max310x_update_best_err(unsigned long f, long *besterr)
 	return 1;
 }
 
-static u32 max310x_set_ref_clk(struct device *dev, struct max310x_port *s,
+static s32 max310x_set_ref_clk(struct device *dev, struct max310x_port *s,
 			       unsigned long freq, bool xtal)
 {
 	unsigned int div, clksrc, pllcfg = 0;
@@ -657,7 +657,8 @@ static u32 max310x_set_ref_clk(struct device *dev, struct max310x_port *s,
 		} while (!stable && (++try < MAX310X_XTAL_WAIT_RETRIES));
 
 		if (!stable)
-			dev_warn(dev, "clock is not stable yet\n");
+			return dev_err_probe(dev, -EAGAIN,
+					     "clock is not stable\n");
 	}
 
 	return bestfreq;
@@ -1282,7 +1283,7 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 {
 	int i, ret, fmin, fmax, freq;
 	struct max310x_port *s;
-	u32 uartclk = 0;
+	s32 uartclk = 0;
 	bool xtal;
 
 	for (i = 0; i < devtype->nr; i++)
@@ -1360,6 +1361,11 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 	}
 
 	uartclk = max310x_set_ref_clk(dev, s, freq, xtal);
+	if (uartclk < 0) {
+		ret = uartclk;
+		goto out_uart;
+	}
+
 	dev_dbg(dev, "Reference clock set to %i Hz\n", uartclk);
 
 	for (i = 0; i < devtype->nr; i++) {