- A fixed extent map (statically allocated descriptor storage) is
created in init386(), just before the call to consinit(). The
fixed descriptor storage has enough room for 8 region entires,
which is plenty for early initialization, but doesn't chew up
that much memory.
This extent map (ioport_ex) manages the i386 i/o port
space (0x0 - 0xffff).
- Just before the call to configure() in cpu_startup(), a
flag is set which notifies the bus_io functions that it is
safe to use malloc() to allocate descriptor storage, in the
event that more than 8 regions are needed.
- bus_io_map() attempts to allocate the specified region from
ioport_ex. If the allocation succeeds, the io handle is
filled in. If the allocation fails, it is implied that
something else is already using that io space, and an
error condition is returned.
- bus_io_unmap() frees a region previously allocated from
ioport_ex in bus_io_map(). If the free fails, a warning
is printed on the conole.
These changes implement "port accounting". This is required for
proper autoconfiguration on the i386 port, and makes dealing with,
among other things, PCMCIA io mappings _much_ easier.
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