KernelTrap: Understanding The Stricter Type Checks

“With the release of 2.6.9-rc2, Linus Torvalds mentioned the
addition of stricter type checks for PCI memory mapping. He has
since followed up with another email to explain these stricter type
checks, ‘this is a background mail mainly for driver writers and/or
architecture people. Or others that are just interested in really
low-level hw access details. Others–please feel free to ignore.’
His lengthy background email was followed by some interesting
discussion, offering further clarification. Linus begins:

“‘The background for this iospace type-checking change is that
we’ve long had some serious confusion about how to access PCI
memory mapped IO (MMIO), mainly because on a PC (and some non-PC’s
too) that IO really does look like regular memory, so you can have
a driver that just accesses a pointer directly, and it will
actually work on most machines…'”

Complete
Story