iomem and ioports

[Rajat Jain]

Some places i have seen that directly IO port is typecasted to  (__iomem * ) and used as it is i.e. returned value is given to ioread and iowrite functions.Kindly explain why in some cases we dont add offset and in some cases we add??
Is it because in some board we need to memory map the port number and then read/write and in some boards we don't need to do that as we can directly access the port using arch specific functions??
 

RAJAT> I would think so.