Enabling Hotplug

[Ravi Paluri (QUIC)]

Hi all,
    We are trying to enable Hotplug functionality. 
We've our device node under "/dev/<device-node>", which gets created at boot-up.
SUBSYSTEM of this <device-node> is "subsys". Hence, I created a folder named "subsys" under "/etc/hotplug.d/" and I added a script at this location as per detailed @ https://openwrt.org/docs/guide-user/base-system/hotplug#usagetroubleshooting

I also modified "/etc/hotplug.json" file with below code but script under "/etc/hotplug.d/subsys" is not getting executed, possibly since we are not getting SUBSYSTEM trigger event?

["if",
         [ "and",
                 [ "eq", "SUBSYSTEM", "subsys" ],
                 [ "isdir", "/etc/hotplug.d/subsys" ]
         ],
         [ "exec", "/sbin/hotplug-call", "subsys" ]
 ],

We've no clue why this trigger event is not getting fired. 
Do we need to enable any kernel configuration flag? (We are using kernel 5.4 version.) or any package needs to selected under openwrt menu etc.
Any pointers on how to enable hotplug will be very helpful.

Thanks,
Ravi