i found this snippet from arch/mips/kernel/head.S breaking DecStations:
@@ -68,9 +76,9 @@
mtc0 k0, CP0_ENTRYLO0 # load it
srl k1, k1, 6 # convert to entrylo1
mtc0 k1, CP0_ENTRYLO1 # load it
- b 1f
- tlbwr # write random tlb entry
+ nop # Need 2 cycles between mtc0
+ nop # and tlbwr (CP0 hazard).
+ tlbwr # write random tlb entry
eret # return from trap
>From the Documentation and how i understand it this is perfectly
valid as the mtc0 instruction causes a cp0 hazard within the next 2 instruction
thought the delay of 2 cycles would be ok.
This is probably related to the Decstations having REALLY old R4000 silicion
revisions - Probably one should look through the erratas for these
flo@repeat:~$ cat /proc/cpuinfo
cpu : MIPS
cpu model : R4000SC V3.0
system type : Digital DECstation 5000/1xx
OK - I just had a look at the errata - This IS a workaround to a
Mips R4000SC 2.0, 3.0 errata - I restored the original code back.
Florian Lohoff email@example.com +49-5201-669912
Why is it called "common sense" when nobody seems to have any?