On Sat, 2004-04-03 at 01:41, John Whitney wrote:

quoted

No, you are not supposed to pass an address coming from
pci_alloc_consistent() to pci_map_single(), period.

Why take that stance, when a simple change to virt_to_phys() makes all
virtual addresses coming from any routine work correctly?  Would that
be far simpler system under which to implement code, with less prone to
error (no need to worry about making sure you have the "correct"
virtual memory type for a given routine - all virtual memory addresses
would work).  This just sounds entirely political, and very little
practical.

No. virt_to_phys() operates on the linear mapping only, that has
always been the case, doing otherwise would be non portable anyway.

I think we should deprecate virt_to_phys() anyway and use __pa in
the arch code, that would avoid people trying to use it for what it
is not.

Regarding pci_map_single(), it's semantics are clear regarding the
kind of memory it can map. Doing a ppc only hack to make the nonsense
work (passing it memory obtained by pci_alloc_consistent) would be
letting drivers writers do the wrong thing on ppc and break whenever
they port the driver to a platform that enforce that limitation.

We could add a runtime check to pci_map_single() to verify it gets
passed an address within the linear mapping though. That would catch
the bugs you are afraid of.

(Oh, and let's keep those discussions on-list).

Ben.


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