TGL: : No video output on external monitor after unplug and re-plug the cable

We found another bug after the fix of #2538 (closed). The external monitor is also connected via WD19's HDMI/DisplayPort just as #2538 (closed). However, the display monitor can only be detected and show output at the very first time we power on the WD19 dock. If we unlplug the cable and replug again, the monitor seems to be detected but there's no video output.

When we power on the WD19 dock with cable connected to the monitor, the drm kernel log shows as follows

Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:intel_get_hpd_pins.isra.0 [i915]] hotplug event received, stat 0x00010000, dig 0x0088888a, pins 0x00000200, long 0x00000200
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:intel_hpd_irq_handler [i915]] digital hpd on [ENCODER:292:DDI D] - long
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:intel_hpd_irq_handler [i915]] Received HPD interrupt on PIN 9 - cnt: 10
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:intel_dp_hpd_pulse [i915]] got hpd irq on [ENCODER:292:DDI D] - long
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:i915_hotplug_work_func [i915]] running encoder hotplug functions
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:i915_hotplug_work_func [i915]] Connector DP-1 (pin 9) received hotplug event. (retry 0)
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:intel_dp_detect [i915]] [CONNECTOR:293:DP-1]
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:intel_power_well_enable [i915]] enabling TC cold off
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:tgl_tc_cold_request [i915]] TC cold block succeeded
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:__intel_tc_port_lock [i915]] Port D/TC#1: TC port mode reset (tbt-alt -> dp-alt)
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:intel_power_well_enable [i915]] enabling AUX D TC1
Apr 20 02:11:53 kernel: [drm:drm_dp_dpcd_read [drm_kms_helper]] AUX D/port D: 0xf0000 AUX -> (ret=  8) 14 1e 40 55 02 00 00 00
Apr 20 02:11:53 kernel: i915 0000:00:02.0: [drm:intel_dp_lttpr_init [i915]] LTTPR common capabilities: 14 1e 40 55 02 00 00 00

Then I replug the cable, the intel_power_well_enable() in intel_dp_aux_xfer() shows enabling DC off power domain instead of enabling AUX D TC1. After that, the flooded i915 0000:00:02.0: [drm:intel_dp_aux_xfer [i915]] AUX D/port D: timeout (status 0x7d4003ff) keeps show up and no video output.

Here's the journal log with kernel boot parameter "drm.debug=0x10e". I power on the dock and see the status become connected at line L353. Unplug the cable at L2683 and replug around L3562. Can anyone suggest what happens at the replug? What can we do to identify the cause? Thanks

wd19_power_discon_conback.log