[console speed] lock console speed to start up speed (#2222)

Auto negotiating console speed could cause sonic to lock on a wrong
speed under rare conditions. The only way to come out of the wrong
speed is to issue line break or restart console service with forced
speed, or reboot sonic.

Lock down the console speed to avoid these situations.

Signed-off-by: Ying Xie <ying.xie@microsoft.com>

files/image_config/platform/rc.local

@@ -85,6 +85,19 @@ update_mgmt_interface_macaddr() {
     sed -i "/eth0/ s/ATTR{address}==\"$old_mac\"/ATTR{address}==\"$new_mac\"/g" /etc/udev/rules.d/70-persistent-net.rules
 }
 
+program_console_speed()
+{
+    speed=$(cat /proc/cmdline | grep -Eo 'console=ttyS[0-9]+,[0-9]+' | cut -d "," -f2)
+    if [ -z "$speed" ]; then
+        CONSOLE_SPEED=9600
+    else
+        CONSOLE_SPEED=$speed
+    fi
+
+    sed -i "s|\-\-keep\-baud .* %I| $CONSOLE_SPEED %I|g" /lib/systemd/system/serial-getty@.service
+    systemctl daemon-reload
+}
+
 # If the machine.conf is absent, it indicates that the unit booted
 # into SONiC from another NOS. Extract the machine.conf from ONIE.
 if [ ! -e /host/machine.conf ]; then
@@ -185,6 +198,8 @@ done
 
 eval sonic_version=$(cat /etc/sonic/sonic_version.yml | grep build_version | cut -f2 -d" ")
 
+program_console_speed
+
 if [ -f /host/image-$sonic_version/platform/firsttime ]; then
 
     if [ -n "$aboot_platform" ]; then