IOS: Do not init libusb unless passthrough is enabled

Source/Core/Core/IOS/USB/Host.cpp

@@ -30,9 +30,6 @@ namespace Device
 {
 USBHost::USBHost(u32 device_id, const std::string& device_name) : Device(device_id, device_name)
 {
-#ifdef __LIBUSB__
-  m_libusb_context = LibusbContext::Get();
-#endif
 }
 
 ReturnCode USBHost::Open(const OpenRequest& request)
@@ -116,10 +113,14 @@ bool USBHost::AddNewDevices(std::set<u64>& new_devices, DeviceChangeHooks& hooks
                             const bool always_add_hooks)
 {
 #ifdef __LIBUSB__
-  if (m_libusb_context)
+  if (SConfig::GetInstance().m_usb_passthrough_devices.empty())
+    return true;
+
+  auto libusb_context = LibusbContext::Get();
+  if (libusb_context)
   {
     libusb_device** list;
-    const ssize_t count = libusb_get_device_list(m_libusb_context.get(), &list);
+    const ssize_t count = libusb_get_device_list(libusb_context.get(), &list);
     if (count < 0)
     {
       WARN_LOG(IOS_USB, "Failed to get device list: %s",
@@ -199,15 +200,29 @@ void USBHost::StartThreads()
   }
 
 #ifdef __LIBUSB__
-  if (m_libusb_context && !m_event_thread_running.IsSet())
+  if (!m_event_thread_running.IsSet())
   {
     m_event_thread_running.Set();
     m_event_thread = std::thread([this] {
       Common::SetCurrentThreadName("USB Passthrough Thread");
+      std::shared_ptr<libusb_context> context;
       while (m_event_thread_running.IsSet())
       {
+        if (SConfig::GetInstance().m_usb_passthrough_devices.empty())
+        {
+          Common::SleepCurrentThread(50);
+          continue;
+        }
+
+        if (!context)
+          context = LibusbContext::Get();
+
+        // If we failed to get a libusb context, stop the thread.
+        if (!context)
+          return;
+
         static timeval tv = {0, 50000};
-        libusb_handle_events_timeout_completed(m_libusb_context.get(), &tv, nullptr);
+        libusb_handle_events_timeout_completed(context.get(), &tv, nullptr);
       }
     });
   }

Source/Core/Core/IOS/USB/Host.h

@@ -71,7 +71,6 @@ private:
   void DispatchHooks(const DeviceChangeHooks& hooks);
 
 #ifdef __LIBUSB__
-  std::shared_ptr<libusb_context> m_libusb_context;
   // Event thread for libusb
   Common::Flag m_event_thread_running;
   std::thread m_event_thread;