Once the module is loaded, the
asus_acpi_add function should be called by the ACPI subsystem if the firmware indicates the system includes a device with a PNP ID of
ATK0101. This is arranged by the module initialization calling
acpi_bus_register_driver with the address of
static struct acpi_driver asus_acpi_driver as a parameter. This structure includes as its
.ids element a table of PNP/ACPI IDs recognized by this driver.
So, the first thing to check would be, if your system has ATK0100 or ATK0101 device IDs.
The result should be a list of PNP IDs, one per line. If the list does not include
ATK0101, then there's a good reason why the module is not getting loaded: the ACPI firmware does not claim to have the interface this module would use.
In your other question on Stack Overflow, you mention that the
asus_wmi module does get auto-detected on your laptop. The WMI interface this module accesses seems to have a lot of miscellaneous functionality, including keyboard backlight control. The features supported by the hardware are apparently indicated by the SFUN value; however, the meaning of only a few bits of the SFUN value is know to the
As a result, the
asus-nb-wmi.c source code file has a list of Asus notebook models and specific settings for the control key driver for each model. It appears that the FX503 is not yet listed in there; if you can compile your own kernels, you might try adding your notebook model to the list and test the quirk values of other Asus notebook models with similar functionality; with luck and persistence, you might find workable settings that way if the hardware/firmware implementation is not too different.
If you manage to do that, please report your results to the author of the
asus_wmi driver: that way your work will also benefit others who have the same model as yours. You'll also get your name added to the long list of Linux kernel contributors.
You might also want to just email the developer of that driver to ask for advice: s/he probably can suggest more specific things to try, if you are willing to make the effort.