diff --git a/Source/Core/InputCommon/ControllerInterface/ControllerInterface.cpp b/Source/Core/InputCommon/ControllerInterface/ControllerInterface.cpp
index afdf768435..c4ef52a2a9 100644
--- a/Source/Core/InputCommon/ControllerInterface/ControllerInterface.cpp
+++ b/Source/Core/InputCommon/ControllerInterface/ControllerInterface.cpp
@@ -37,6 +37,10 @@
 
 ControllerInterface g_controller_interface;
 
+// We need to save which input channel we are in by thread, so we can access the correct input
+// update values in different threads by input channel. We start from InputChannel::Host on all
+// threads as hotkeys are updated from a worker thread, but UI can read from the main thread. This
+// will never interfere with game threads.
 static thread_local ciface::InputChannel tls_input_channel = ciface::InputChannel::Host;
 
 void ControllerInterface::Initialize(const WindowSystemInfo& wsi)
@@ -272,7 +276,11 @@ void ControllerInterface::UpdateInput()
   {
     std::lock_guard lk(m_devices_mutex, std::adopt_lock);
     for (const auto& d : m_devices)
+    {
+      // Theoretically we could avoid updating input on devices that don't have any references to
+      // them, but in practice a few devices types could break in different ways, so we don't
       d->UpdateInput();
+    }
   }
 }
 
diff --git a/Source/Core/InputCommon/ControllerInterface/ControllerInterface.h b/Source/Core/InputCommon/ControllerInterface/ControllerInterface.h
index 12d17614da..024548b713 100644
--- a/Source/Core/InputCommon/ControllerInterface/ControllerInterface.h
+++ b/Source/Core/InputCommon/ControllerInterface/ControllerInterface.h
@@ -67,6 +67,9 @@ public:
   void Shutdown();
   void AddDevice(std::shared_ptr<ciface::Core::Device> device);
   void RemoveDevice(std::function<bool(const ciface::Core::Device*)> callback);
+  // This is mandatory to use on device populations functions that can be called concurrently by
+  // more than one thread, or that are called by a single other thread.
+  // Without this, our devices list might end up in a mixed state.
   void PlatformPopulateDevices(std::function<void()> callback);
   bool IsInit() const { return m_is_init; }
   void UpdateInput();
diff --git a/Source/Core/InputCommon/ControllerInterface/CoreDevice.h b/Source/Core/InputCommon/ControllerInterface/CoreDevice.h
index c368578949..1994cb402c 100644
--- a/Source/Core/InputCommon/ControllerInterface/CoreDevice.h
+++ b/Source/Core/InputCommon/ControllerInterface/CoreDevice.h
@@ -227,6 +227,7 @@ public:
                                           std::chrono::milliseconds maximum_wait) const;
 
 protected:
+  // Exclusively needed when reading/writing "m_devices"
   mutable std::recursive_mutex m_devices_mutex;
   std::vector<std::shared_ptr<Device>> m_devices;
 };
diff --git a/Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.cpp b/Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.cpp
index ebe2e84286..bc1820b8ad 100644
--- a/Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.cpp
+++ b/Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.cpp
@@ -91,6 +91,11 @@ KeyboardMouse::~KeyboardMouse()
 {
   s_keyboard_mouse_exists = false;
 
+  // Independently of the order in which we do these, if we put a breakpoint on Unacquire() (or in
+  // any place in the call stack before this), when refreshing devices from the UI, on the second
+  // attempt, it will get stuck in an infinite (while) loop inside dinput8.dll. Given that it can't
+  // be otherwise be reproduced (not even with sleeps), we can just ignore the problem.
+
   // kb
   m_kb_device->Unacquire();
   m_kb_device->Release();
diff --git a/Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.h b/Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.h
index ceda59d02c..3bd073a6f1 100644
--- a/Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.h
+++ b/Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.h
@@ -34,6 +34,7 @@ private:
     RelativeMouseState relative_mouse;
   };
 
+  // Keyboard key
   class Key : public Input
   {
   public:
@@ -46,6 +47,7 @@ private:
     const u8 m_index;
   };
 
+  // Mouse button
   class Button : public Input
   {
   public:
@@ -58,6 +60,7 @@ private:
     const u8 m_index;
   };
 
+  // Mouse movement offset axis. Includes mouse wheel
   class Axis : public Input
   {
   public:
@@ -72,6 +75,7 @@ private:
     const u8 m_index;
   };
 
+  // Mouse from window center
   class Cursor : public Input
   {
   public: