libhwc2.1: fix ExynosExternalDisplay::disable()

When DP cable is connected, the initial state of external display is:
mHpdStatus = true
mEnabled = false

External display will remain in the above state until DP mirroring
has been confirmed via UI dialog.

If DP cable is disconnected in this state, or if the sink unexpectedly
sends a quick HPD unplug event, external display state changes back to:
mHpdStatus = false
mEnabled = false

and SurfaceFlinger subsequently calls:
ExynosExternalDisplay::setPowerMode(OFF)
  ExynosExternalDisplay::disable()

We need to do full power-down in disable() when mHpdStatus = false.
We cannot skip it just because mEnabled = false.

This change fixes the handling of unexpected rapid sequence of:
HPD plug -> HPD unplug -> HPD plug
that various sinks and hubs use to reset their internal state.

Bug: 310693327
Test: manual testing with USB hub and monitor
Change-Id: Ieffea865b19c802c6903591a2356a7ccb3c1775d

1 files changed, 9 insertions, 4 deletions

diff --git a/libhwc2.1/libexternaldisplay/ExynosExternalDisplay.cpp b/libhwc2.1/libexternaldisplay/ExynosExternalDisplay.cpp
index 84a6971..6aa34db 100644
--- a/libhwc2.1/libexternaldisplay/ExynosExternalDisplay.cpp
+++ b/libhwc2.1/libexternaldisplay/ExynosExternalDisplay.cpp
@@ -448,11 +448,16 @@ int ExynosExternalDisplay::disable()
 {
     ALOGI("[ExternalDisplay] %s +", __func__);
 
-    if (!mEnabled)
-        return HWC2_ERROR_NONE;
-
     if (mHpdStatus) {
-        clearDisplay(false);
+        /*
+         * DP cable is connected and link is up
+         *
+         * Currently, we don't power down here for two reasons:
+         * - power up would require DP link re-training (slow)
+         * - DP audio can continue playing while display is blank
+         */
+        if (mEnabled)
+            clearDisplay(false);
         return HWC2_ERROR_NONE;
     }