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powerpc/booke: Use power-of-two mappings in 64-bit pmap_mapdev

Authored by jhibbits on Apr 1 2020, 2:12 AM.



This reduces the precious TLB1 entry consumption (64 possible in
existing 64-bit cores), by adjusting the size and alignment of a device
mapping to a power of 2, to encompass the full mapping and its

One caveat with this: If a mapping really is smaller than a power of 2,
it's possible to get a machine check or hang if the 'missing' physical
space is accessed. In practice this should not be an issue for users,
as devices overwhelmingly have physical spaces on power-of-two sizes and
alignments, and any design that includes devices which don't follow this
can be addressed by undefining the POW2_MAPPINGS guard.

Diff Detail

rS FreeBSD src repository
Automatic diff as part of commit; lint not applicable.
Automatic diff as part of commit; unit tests not applicable.

Event Timeline

Works for me on RB800 and X5000.

2625 ↗(On Diff #70085)

Does this need ::: "memory" or does clang pick up on the side effects already?

This revision is now accepted and ready to land.Apr 10 2020, 9:37 PM