ioremap reposted

I repost this subject again. and try get some discussion.

ioremap to map a block physical address.

My question how do I do if that piece o memory is already mapped or
not. For exmaple, if I in looking arround in kernel space, and I want
check a phsical memory, I should so a ioremap to get the memory mapped.
However, who know if that block of memory is hanled by another driver
or not. If it is, most like the meory has been alreay mapped by some
driver before.

So the question is, if I can ioremap again, does it harm? and plus, how
happend if I do iounmap afterword, and that if the meory was mapped at
first by some other driver, does that harm?