From a279a87bdb1c5a4682770427031a5ebd4f5101be Mon Sep 17 00:00:00 2001
From: Geoffrey McRae <geoff@hostfission.com>
Date: Thu, 6 Aug 2026 23:05:45 +1000
Subject: [PATCH] [idd] config: reload persisted display modes

Rebuild the driver's cached mode list before replugging the monitor so
Windows enumerates the settings saved by the helper.

Keep saved mode refresh rates intact and update only ExtraMode to the
configured default refresh.
---
 idd/LGIdd/CIndirectDeviceContext.cpp | 51 ++++++++++++++++++++++++----
 idd/LGIdd/CIndirectDeviceContext.h   |  6 ++++
 idd/LGIdd/CPipeServer.cpp            |  2 +-
 idd/LGIdd/CSettings.cpp              | 17 +++++++---
 idd/LGIdd/CSettings.h                |  2 +-
 5 files changed, 65 insertions(+), 13 deletions(-)

diff --git a/idd/LGIdd/CIndirectDeviceContext.cpp b/idd/LGIdd/CIndirectDeviceContext.cpp
index 7e0dc0ae..de4b68c8 100644
--- a/idd/LGIdd/CIndirectDeviceContext.cpp
+++ b/idd/LGIdd/CIndirectDeviceContext.cpp
@@ -635,6 +635,39 @@ void CIndirectDeviceContext::ReplugMonitor()
     m_finishInitQueued.store(1);
 }
 
+void CIndirectDeviceContext::ReloadSettings()
+{
+  bool modesLoaded = false;
+
+  AcquireSRWLockExclusive(&m_modeReloadLock);
+
+  CSettings::DisplayMode extraMode;
+  if (g_settings.GetExtraMode(extraMode))
+  {
+    const unsigned refresh = g_settings.GetDefaultRefresh();
+    if (extraMode.refresh != refresh)
+    {
+      extraMode.refresh = refresh;
+      if (!g_settings.SetExtraMode(extraMode))
+      {
+        ReleaseSRWLockExclusive(&m_modeReloadLock);
+        return;
+      }
+    }
+  }
+
+  modesLoaded = PopulateDefaultModes();
+  ReleaseSRWLockExclusive(&m_modeReloadLock);
+
+  if (!modesLoaded)
+  {
+    DEBUG_ERROR("Failed to reload the display mode list");
+    return;
+  }
+
+  ReplugMonitor();
+}
+
 void CIndirectDeviceContext::OnMonitorDestroyed(IDDCX_MONITOR monitor)
 {
   AcquireSRWLockExclusive(&m_stateLock);
@@ -936,19 +969,23 @@ void CIndirectDeviceContext::SetResolution(uint32_t width, uint32_t height)
   mode.refresh   = g_settings.GetDefaultRefresh();
   mode.preferred = true;
 
-  AcquireSRWLockExclusive(&m_stateLock);
-  m_setMode   = mode;
-  m_doSetMode = true;
-  ReleaseSRWLockExclusive(&m_stateLock);
+  bool modesLoaded = false;
+  AcquireSRWLockExclusive(&m_modeReloadLock);
+  if (g_settings.SetExtraMode(mode))
+    modesLoaded = PopulateDefaultModes();
+  ReleaseSRWLockExclusive(&m_modeReloadLock);
 
-  g_settings.SetExtraMode(mode);
-
-  if (!PopulateDefaultModes())
+  if (!modesLoaded)
   {
     DEBUG_ERROR("Failed to rebuild the display mode list");
     return;
   }
 
+  AcquireSRWLockExclusive(&m_stateLock);
+  m_setMode   = mode;
+  m_doSetMode = true;
+  ReleaseSRWLockExclusive(&m_stateLock);
+
   // IddCxMonitorUpdateModes[2] does not invalidate Windows' cached mode list,
   // so the only reliable way to apply a new mode is to depart and re-arrive the
   // monitor, forcing Windows to rebuild the topology from the new mode list.
diff --git a/idd/LGIdd/CIndirectDeviceContext.h b/idd/LGIdd/CIndirectDeviceContext.h
index 358ba8dd..9dbaae1b 100644
--- a/idd/LGIdd/CIndirectDeviceContext.h
+++ b/idd/LGIdd/CIndirectDeviceContext.h
@@ -215,6 +215,11 @@ private:
   // Never held across an IddCx API call - snapshot then call.
   mutable SRWLOCK m_modeLock = SRWLOCK_INIT;
 
+  // Serializes registry-backed mode changes with rebuilding m_displayModes.
+  // Reload requests arrive on the pipe thread while dynamic resolution
+  // requests arrive on the LGMP timer thread.
+  SRWLOCK m_modeReloadLock = SRWLOCK_INIT;
+
   CSettings::DisplayModes m_displayModes;
   CEdid                   m_edid;
 
@@ -238,6 +243,7 @@ public:
   void InitAdapter();
   void FinishAdapterInit(UINT connectorIndex);
   void FinishInit(UINT connectorIndex);
+  void ReloadSettings();
   void ReplugMonitor();
 
   void OnMonitorDestroyed(IDDCX_MONITOR monitor);
diff --git a/idd/LGIdd/CPipeServer.cpp b/idd/LGIdd/CPipeServer.cpp
index 24fab90b..cee504aa 100644
--- a/idd/LGIdd/CPipeServer.cpp
+++ b/idd/LGIdd/CPipeServer.cpp
@@ -262,7 +262,7 @@ void CPipeServer::HandleReloadSettings()
 
   AcquireSRWLockShared(&m_deviceContextLock);
   if (m_deviceContext)
-    m_deviceContext->ReplugMonitor();
+    m_deviceContext->ReloadSettings();
   ReleaseSRWLockShared(&m_deviceContextLock);
 }
 
diff --git a/idd/LGIdd/CSettings.cpp b/idd/LGIdd/CSettings.cpp
index ae3bd03c..4bab5d8c 100644
--- a/idd/LGIdd/CSettings.cpp
+++ b/idd/LGIdd/CSettings.cpp
@@ -76,7 +76,7 @@ CSettings::DisplayModes CSettings::LoadModes()
   return displayModes;
 }
 
-void CSettings::SetExtraMode(const DisplayMode& mode)
+bool CSettings::SetExtraMode(const DisplayMode& mode)
 {
   WCHAR buf[64];
   _snwprintf_s(buf, _countof(buf), _TRUNCATE, L"%ux%u@%u%s",
@@ -94,15 +94,24 @@ void CSettings::SetExtraMode(const DisplayMode& mode)
 
   if (ec != ERROR_SUCCESS)
   {
-    DEBUG_INFO("Failed to write key");
-    return;
+    DEBUG_ERROR_HR(ec, "Failed to open settings key for ExtraMode");
+    return false;
   }
 
   const WCHAR* valueName = L"ExtraMode";
   const DWORD  cb = (DWORD)((wcslen(buf) + 1) * sizeof(WCHAR));
 
-  RegSetValueExW(hKey, valueName, 0, REG_SZ, (const BYTE*)buf, cb);
+  ec = RegSetValueExW(hKey, valueName, 0, REG_SZ,
+    (const BYTE*)buf, cb);
   RegCloseKey(hKey);
+
+  if (ec != ERROR_SUCCESS)
+  {
+    DEBUG_ERROR_HR(ec, "Failed to write ExtraMode");
+    return false;
+  }
+
+  return true;
 }
 
 std::wstring CSettings::ReadStringValue(const wchar_t* name, const wchar_t* defaultValue)
diff --git a/idd/LGIdd/CSettings.h b/idd/LGIdd/CSettings.h
index f31a763e..7b932557 100644
--- a/idd/LGIdd/CSettings.h
+++ b/idd/LGIdd/CSettings.h
@@ -39,7 +39,7 @@ class CSettings
     CSettings();
 
     DisplayModes LoadModes();
-    void SetExtraMode(const DisplayMode & mode);
+    bool SetExtraMode(const DisplayMode & mode);
     bool GetExtraMode(DisplayMode & mode);
     unsigned GetDefaultRefresh() const;