linux-kernel - [PATCH 4/4] serial: max310x: prevent infinite while() loop in port startup

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Message-Id: <20240116213001.3691629-5-hugo@hugovil.com>
Date: Tue, 16 Jan 2024 16:30:01 -0500
From: Hugo Villeneuve <hugo@...ovil.com>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	jan.kundrat@...net.cz,
	shc_work@...l.ru
Cc: linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	hugo@...ovil.com,
	Hugo Villeneuve <hvilleneuve@...onoff.com>,
	stable@...r.kernel.org
Subject: [PATCH 4/4] serial: max310x: prevent infinite while() loop in port startup

From: Hugo Villeneuve <hvilleneuve@...onoff.com>

If there is a problem after resetting a port, the do/while() loop that
checks the default value of DIVLSB register may run forever and spam the
I2C bus.

Add a delay before each read of DIVLSB, and a maximum number of tries to
prevent that situation from happening.

Also fail probe if port reset is unsuccessful.

Fixes: 10d8b34a4217 ("serial: max310x: Driver rework")
Cc: <stable@...r.kernel.org>
Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
---
 drivers/tty/serial/max310x.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index 552e153a24e0..10bf6d75bf9e 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -237,6 +237,10 @@
 #define MAX310x_REV_MASK		(0xf8)
 #define MAX310X_WRITE_BIT		0x80
 
+/* Port startup definitions */
+#define MAX310X_PORT_STARTUP_WAIT_RETRIES	20 /* Number of retries */
+#define MAX310X_PORT_STARTUP_WAIT_DELAY_MS	10 /* Delay between retries */
+
 /* Crystal-related definitions */
 #define MAX310X_XTAL_WAIT_RETRIES	20 /* Number of retries */
 #define MAX310X_XTAL_WAIT_DELAY_MS	10 /* Delay between retries */
@@ -1346,6 +1350,9 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 		goto out_clk;
 
 	for (i = 0; i < devtype->nr; i++) {
+		bool started = false;
+		unsigned int try = 0, val = 0;
+
 		/* Reset port */
 		regmap_write(regmaps[i], MAX310X_MODE2_REG,
 			     MAX310X_MODE2_RST_BIT);
@@ -1354,8 +1361,17 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 
 		/* Wait for port startup */
 		do {
-			regmap_read(regmaps[i], MAX310X_BRGDIVLSB_REG, &ret);
-		} while (ret != 0x01);
+			msleep(MAX310X_PORT_STARTUP_WAIT_DELAY_MS);
+			regmap_read(regmaps[i], MAX310X_BRGDIVLSB_REG, &val);
+
+			if (val == 0x01)
+				started = true;
+		} while (!started && (++try < MAX310X_PORT_STARTUP_WAIT_RETRIES));
+
+		if (!started) {
+			ret = dev_err_probe(dev, -EAGAIN, "port reset failed\n");
+			goto out_uart;
+		}
 
 		regmap_write(regmaps[i], MAX310X_MODE1_REG, devtype->mode1);
 	}
-- 
2.39.2