You’re right and I agree there are problems with this approach. However,
there are cases where it really isn’t a problem. In fact, I’m working on
such a project right now. We are designing a device that has shared RAM
mapped to one of its PCI memory regions. My driver is going to do nothing
more than determine the correct offset address and copy lots of
user-supplied buffers to/from the PCI device. Since it is all user data
anyway, this is a perfect example of where directly mapping a PCI region
into user memory space would make the driver almost trivial. I wouldn’t
dream of mapping the “control” regions of the device to user mode. Also,
this is in an embedded application, so many of the normal concerns don’t
apply here. In 99.99% of the cases, I agree that directly mapping PCI
registers is a bad idea for all the reasons stated.
Greg
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