ow to define an uncached linker region

Since IO areas should never be accessed by cacheable memory accesses this is all rather moot.

More likely is that, somewhere, you 'forget' to use the correct access function and do a cacheable access well after initialisation.

If you are allocating memory descriptors that will be accessed by other bus masters then you also need to ensure that the area you use doesn't start/end in the middle of a cache line - otherwise other users might cause the cache line to be dirty.

OTOH if you are reserving large chunks of memory in the physical memory map (not a run time), then you really don't need to worry about them being cached before you start.

But, yes, problems with unexpected cache operations can be very difficult to resolve.