[PATCH 5.4 33/51] serial: max310x: prevent infinite while() loop in port startup

[Sasha Levin <sashal@kernel.org>]

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

[ Upstream commit b35f8dbbce818b02c730dc85133dc7754266e084 ]

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@vger.kernel.org
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20240116213001.3691629-5-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 80298a5714bcb..978d9d93127e5 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -235,6 +235,10 @@
 #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 */
@@ -1316,6 +1320,9 @@ 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);
@@ -1324,8 +1331,17 @@ 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);
 	}
-- 
2.43.0