Re: [PATCH] TX49 MFC0 bug workaround

[Atsushi Nemoto <anemo@mba.ocn.ne.jp>]

>>>>> On Fri, 03 Feb 2006 05:26:48 +0300, Sergei Shtylylov 
>>>>> <sshtylyov@ru.mvista.com> said:
sshtylyov>     And.. how do you imagine placing a NOP (which surely
sshtylyov> just moves MFC0 down so that it's a 1st insn. on the next
sshtylyov> page). What if it'll move it to the errata prone address
sshtylyov> from a safe one instead?

The NOP will break the "If mfc0 $12 follows store" condition.

Actually, the condition is more strict.  This is a code sequence from
the errata. (It seems English version is not updated yet...)

        Load/Store instruction
        Load/Store/Sync instruction
        Mfc0 rt,rd      ; rd is Status/Cause
        -- page boundary --
        nop             ; TLB mapped area

For Cause register case, Linux modules should never read it so it
would not be a problem.

---
Atsushi Nemoto