iomem and ioports

[prabhu]

HI All,

I started to understand output of /proc/oiports and /proc/iomem. I 
confused to relate these two's output. 

Below is the kernel source for Mapping of io-port to io-mem. Could 
anyone please explain below code.

/* We encode the physical PIO addresses (0-0xffff) into the
                                           (0-
 * pointer by offsetting them with a constant (0x10000) and
 * assuming that all the low addresses are always PIO. That means
                                                            means
 * we can do some sanity checks on the low bits, and don't
 * need to just take things for granted.
 */
#define PIO_OFFSET              0x10000UL
#define PIO_MASK                0x0ffffUL
#define PIO_RESERVED            0x40000UL
void __iomem *ioport_map(unsigned long port, unsigned int nr) {
     __iomem
           if (port > PIO_MASK) return NULL;
           return (void __iomem *) (unsigned long) (port + PIO_OFFSET);
                        __iomem
}

Thanks,
Prabhu
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