X11: search all XI2 touch devices, not just masters (thanks, Volumetic!). Otherwise, you won't find touch devices that aren't currently assigned to a system cursor.
diff --git a/src/video/x11/SDL_x11xinput2.c b/src/video/x11/SDL_x11xinput2.c
index 5cb7109..db439ba 100644
--- a/src/video/x11/SDL_x11xinput2.c
+++ b/src/video/x11/SDL_x11xinput2.c
@@ -183,7 +183,7 @@ X11_InitXinput2Multitouch(_THIS)
SDL_VideoData *data = (SDL_VideoData *) _this->driverdata;
XIDeviceInfo *info;
int ndevices,i,j;
- info = X11_XIQueryDevice(data->display, XIAllMasterDevices, &ndevices);
+ info = X11_XIQueryDevice(data->display, XIAllDevices, &ndevices);
for (i = 0; i < ndevices; i++) {
XIDeviceInfo *dev = &info[i];