Messages in this thread | | | Date | Tue, 27 Jan 2004 10:18:58 -0700 | From | Tom Rini <> | Subject | Re: Using 8 Instruction and Data BAT registers in 82xx |
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On Mon, Jan 26, 2004 at 10:29:41AM -0800, Dave Johnson wrote: > > Hi All: > As there are 8 data and Instruction BAT registers in > some 82xx flavors, and Cort has posted a patch to ADD > these registers > (http://www.ussg.iu.edu/hypermail/linux/kernel/0209.1/0871.html) > I was wondering if anyone has any idea how to use > these addistional BAT regs be used?? Perhaps for new > processes and threads, etc.
Step one would be to audit the usages of the 8_BATS feature to ensure that they'll be fine if invoked on an 82xx with 8 BATS. It's almost certainly going to be true, but should still be done.
Step two would be to distinguish the 82xx's with 8 BATs from the ones that don't. I don't know if these have a different PVR, but I hope they do, otherwise it'll be harder (but not impossible certainly) to.
Finally, as you've probably surmised, all that we do with these additional BATs is to clear them out. It could be possible to extend io_block_mapping to make use of these additional BATs (and v_mapped_by_bats/p_mapped_by_bats, etc).
Trying to do processes and/or threads (i.e. userland stuff) becomes a giant pain (per-context BAT mappings have to be tracked), there's lots of security implications to keep in mind, and of course the overhead of doing all of this will probably cancel out any speed gain you would have otherwise gotten.
-- Tom Rini http://gate.crashing.org/~trini/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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