Why does request_mem_region() work fine on 32 bit Linux but return NULL on 64 bit?

Question

linux

There is a device pci driver, it has a request_mem_region() call. On 32-bit Linux everything works correctly, but on 64-bit Linux it returns NULL. What could be the reason?

Answer 1

The requested memory may have already been allocated to another device. See /proc/iomem