Linux device model: Same device but different drivers-Collection of common programming errors

Your problem is quite easily solved. The 5 UART devices are presently registered at kernel startup and their function is locked. This is now how it normally works for PCI or USB devices, right? So what you need to do is pull the device registration out of the startup code and register it dynamically. You can even register/unregister as needed.

at91_register_uart() is being called from your board file for every UART that needs registered. at91_add_device_serial() will then platform_device_register all those you what setup. One solution is to let at91_register_uart() be called for all 5 UARTS, but then remove the call to at91_add_device_serial() from your board. You can then make it an exported function that can be called by your loadable drivers. You can even add an argument to it (int) so that instead of looping on all UARTS, you can select which ones to register individually. You can also mirror this function by making one that unregisters the devices.

NOTE: I think you’ll need to always leave one UART dedicated as your console, if you are using one that way. You could probably hide that in the exported function by only allowing index 0->3 as in input and then mapping 0->3 to 0-4, skipping the UART that you want to use for console.