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Mapping I/O memory in virtual memory
Load/store instructions work with virtual addresses
To access I/O memory, drivers need to have a virtual address that the processor can handle, because I/O memory is not mapped by default in virtual memory.
The ioremap functions satisfy this need:
void *ioremap(unsigned long phys_addr,
unsigned long size);
void iounmap(void *address);
Caution: check that ioremap doesn't return a NULL address!