[PATCH] hwmon: (aspeed-g6-pwm-tach) Guard fan RPM calculation against divide-by-zero

[Guenter Roeck <linux@roeck-us.net>]

Sashiko reports:

In the aspeed-g6-pwm-tacho driver, the aspeed_tach_val_to_rpm() function
calculates the fan RPM using the tachometer value. However, it does not
check if the tachometer value is zero before performing the division.

If the hardware reports a tachometer value of 0 (which can happen due to
an extremely fast pulse, a stuck edge, or a hardware glitch), the
calculated tach_div evaluates to 0. The subsequent call to do_div() with
tach_div as the divisor triggers a divide-by-zero exception, leading to
a kernel panic.

Check the divisor against zero to fix the problem.

Fixes: 7e1449cd15d1 ("hwmon: (aspeed-g6-pwm-tacho): Support for ASPEED g6 PWM/Fan tach")
Cc: Billy Tsai <billy_tsai@aspeedtech.com>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/aspeed-g6-pwm-tach.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/aspeed-g6-pwm-tach.c b/drivers/hwmon/aspeed-g6-pwm-tach.c
index 4f6e6d440dd4..5d611a8e5269 100644
--- a/drivers/hwmon/aspeed-g6-pwm-tach.c
+++ b/drivers/hwmon/aspeed-g6-pwm-tach.c
@@ -293,7 +293,10 @@ static int aspeed_tach_val_to_rpm(struct aspeed_pwm_tach_data *priv, u32 tach_va
 		priv->clk_rate, tach_val, tach_div);
 
 	rpm = (u64)priv->clk_rate * 60;
-	do_div(rpm, tach_div);
+	if (tach_div)
+		do_div(rpm, tach_div);
+	else
+		rpm = 0;
 
 	return (int)rpm;
 }
-- 
2.45.2