With Debian, the X11 config file can automatically filled with default values after a dpkg-reconfigure xserver-xorg.
If any X11-related error occurs, some lines are added to the X11 default log file : /var/log/Xorg.0.log
There are several levels of warnings : EE for error, WW for warning and here II for informational.
In order to have a X11 config file very close to my hardware and software configuration, I try to remove any message such as this one below :
(II) Cannot locate a core pointer device.
(II) Cannot locate a core keyboard device.
(II) The server relies on HAL to provide the list of input devices.
If no devices become available, reconfigure HAL or disable AllowEmptyInput.
To avoid having this lines each time the X11 server is started, you have to add these information to your X11 config file in the “Server Flags” section :
Option “AllowEmptyInput” “off”
To see the changes, restart your X11 server and check your X11 log file.