From 901e2568fe382115e7aac711b5f52ba6501645b7 Mon Sep 17 00:00:00 2001
From: OBattler <oubattler@gmail.com>
Date: Thu, 29 Feb 2024 06:46:37 +0100
Subject: [PATCH] Mask out serial passthrough MSR bits when in loopback mode,
 fixes #4217.

---
 src/device/serial.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/device/serial.c b/src/device/serial.c
index 37aadf8fe..dcdffb71c 100644
--- a/src/device/serial.c
+++ b/src/device/serial.c
@@ -686,7 +686,10 @@ serial_read(uint16_t addr, void *priv)
             serial_update_ints(dev);
             break;
         case 6:
-            ret = dev->msr | dev->msr_set;
+            if (dev->mctrl & 0x10)
+                ret = dev->msr;
+            else
+                ret = dev->msr | dev->msr_set;
             dev->msr &= ~0x0f;
             dev->int_status &= ~SERIAL_INT_MSR;
             serial_update_ints(dev);