Re: PATCH: support for Arctic/Beech/Ebony

Joakim Tjernlund
2003-01-30T22:06:23Z

Hi again :-)

> At 03:23 AM 1/30/2003, you wrote:
> > > Joakim,
> > >
> > > At 01:46 PM 1/29/2003, you wrote:
> > > > - You don't need mb() since ioremap will add the
> > > > GUARDED attribute to the mapping.
> > >
> > > Well, this is not quite correct.
> > >
> > > GUARDED attribute does _NOT_ prevent reordering of loads and stores on PPC
> > > (on 4xx at least).
> > >
> > > See comments in asm-ppc/system.h and also IBM app note "Software
> > > consideration when migrating to the PowerPC 440GP from 405GP"
> > >
> >
> >hmm, maybe it's specific to the 8xx family. 860 and 862 does not do
> >speculative accesses on GUARDED memory.
>
> It does! But speculative accesses and access reordering are not the same
> thing :)

what do you mean, does or does not do speculative accesses?

>
> There is a subtle difference.

Yes I understand now, but I discussed this with my HW contact at Motorola and he agreed
that it was OK to remove the mb(). Maybe he was wrong or perhaps non speculative accesses
on mpc 860/862 also disables reorder? I can not find any statement that confirms this.

Howerver I have been running our boards without the mb()'s for months now, no problem with
it so far.

Jocke

PS.
Does the PREEMPT patch still work for you? I havn't seen any problems here yet.