FAILED: patch "[PATCH] serial: max310x: prevent infinite while() loop in port" failed to apply to 5.15-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x b35f8dbbce818b02c730dc85133dc7754266e084
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2024021928-flanked-outboard-6a4c@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

b35f8dbbce81 ("serial: max310x: prevent infinite while() loop in port startup")
93cd256ab224 ("serial: max310x: improve crystal stable clock detection")
0419373333c2 ("serial: max310x: set default value when reading clock ready bit")
6ef281daf020 ("serial: max310x: use a separate regmap for each port")
285e76fc049c ("serial: max310x: use regmap methods for SPI batch operations")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From b35f8dbbce818b02c730dc85133dc7754266e084 Mon Sep 17 00:00:00 2001
From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
Date: Tue, 16 Jan 2024 16:30:01 -0500
Subject: [PATCH] serial: max310x: prevent infinite while() loop in port
 startup

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@xxxxxxxxxxxxxxx
Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240116213001.3691629-5-hugo@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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);
 	}