RK3576: Switch audio to DP sink on Alt Mode connection

When a DP Alt Mode display is connected, save the current PipeWire
default sink and switch to the DP audio sink (identified by the DP
controller address 27e40000 in the PipeWire sink node name). Restore
the saved sink on disconnect.

The DP audio sink is created automatically at kernel probe time by the
DRM_BRIDGE_OP_DP_AUDIO framework (hdmi-audio-codec platform device).
The exact PipeWire sink name may need adjustment after first-boot
testing, but the 27e40000 pattern should match it uniquely since the
internal ES8388 codec is on a different bus address.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: pgratz1

projects/ROCKNIX/packages/sysutils/system-utils/sources/scripts/dp_monitor

@@ -17,6 +17,7 @@
 ls /sys/class/drm/card*-DP-* /sys/class/drm/card*-HDMI-A-* 2>/dev/null | grep -q . || exit 0
 
 _LAST_STATE="init"
+_SAVED_AUDIO_SINK=""
 
 _get_active_externals() {
     wlr-randr 2>/dev/null | awk '
@@ -30,6 +31,13 @@ _get_all_internals() {
     wlr-randr 2>/dev/null | awk '/^(DSI|eDP|LVDS)-/ { print $1 }'
 }
 
+# Returns the PipeWire sink for DP audio (hdmi-audio-codec on 27e40000.dp).
+# The sink node name includes the DP controller address after the framework
+# creates an hdmi-audio-codec platform device at probe time.
+_get_dp_audio_sink() {
+    pactl list short sinks 2>/dev/null | awk '/27e40000/ { print $2; exit }'
+}
+
 _apply() {
     local state="internal"
     [ -n "$(_get_active_externals)" ] && state="external"
@@ -48,12 +56,20 @@ _apply() {
         fi
         # Stop USB gadget: its data lanes conflict with DP Alt Mode on RK3576
         systemctl is-active --quiet usbgadget && systemctl stop usbgadget
+        # Switch audio output to DP sink; save current default to restore later
+        local dp_sink
+        _SAVED_AUDIO_SINK=$(pactl get-default-sink 2>/dev/null || true)
+        dp_sink=$(_get_dp_audio_sink)
+        [ -n "$dp_sink" ] && pactl set-default-sink "$dp_sink" 2>/dev/null || true
     else
         # Only re-enable internal panels on actual disconnect, not first-boot
         if [ "$prev" != "init" ]; then
             while IFS= read -r out; do
                 wlr-randr --output "$out" --preferred --on 2>/dev/null
             done < <(_get_all_internals)
+            # Restore saved audio sink
+            [ -n "$_SAVED_AUDIO_SINK" ] && pactl set-default-sink "$_SAVED_AUDIO_SINK" 2>/dev/null || true
+            _SAVED_AUDIO_SINK=""
         fi
     fi