Re: [linux-mac68k] Re: PowerBook 540c
On Tue, Oct 26, 2004 at 09:16:35PM +1000, Finn Thain wrote:
> As someone else pointed out recently, just having some way to determine
> the presence or absence of the bug would be good.
Well, I don't know enough about the memory management code to write it,
but a basic outline of a test that should work would be as follows:
create a page filled with NOP, and set the last word to an FPU instruction
(must be an emulated/non-existent instruction)
set the next page after it to exist, but be flagged as swapped out
start up a thread on the page leading up to the FPU instruction
if both the FPU handler and the page fault get called, the chip is good
My understanding of the bug is that the page fault handler gets called
during instruction prefetch and the current machine state isn't properly
preserved. This causes the emulated instruction to act like it completed,
but the handler was not actually called. It leaves the chip in any of a
number of unexpected states leading to errors.
> NCR5380 support is broken in 2.6.8.1 (AFAICT -- meaning, it is reported
> broken on IIfx, and I've confirmed than on an LC III). Maybe the PB 540c
> has IDE as well, or doesn't suffer the same bug for some reason... it is
> worth a try.
Well, the NCR5380 bug seems to be tied to interrupt handling, so it's
possible that it only affects a subset of models.
Brad Boyer
flar@allandria.com
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