ioremap questions

[Yoav Steinberg]

Hello,
i'm trying to map a physical address on the 440GP's external bus to a virtual address so I can access it from kernel space. While looking at the ebony.c file under the drivers/mtd/maps I saw that a function called ioremap64 was used.
My questions:
1) Why use the ioremap64 function which receives a 64bit physical address when the CPU is a 32 bit CPU? It seems like this is a special function for th 44x series, is this true?
2) There seem to be multiple ioremap functions: ioremap/64/_nocache etc. which is the most appropriate one? What are the differences?
3) Do I need to call iounmap before remapping somethig previouslly mapped with ioremap?
 
Thank's
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