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SubjectRe: [PATCH v5 1/5] powerpc/85xx: implement hardware timebase sync
On Tue, Jun 05, 2012 at 11:07:41AM -0500, Scott Wood wrote:
> On 06/05/2012 04:08 AM, Zhao Chenhui wrote:
> > On Fri, Jun 01, 2012 at 10:40:00AM -0500, Scott Wood wrote:
> >> I know you say this is for dual-core chips only, but it would be nice if
> >> you'd write this in a way that doesn't assume that (even if the
> >> corenet-specific timebase freezing comes later).
> >
> > At this point, I have not thought about how to implement the cornet-specific timebase freezing.
>
> I wasn't asking you to. I was asking you to not have logic that breaks
> with more than 2 CPUs.

These routines only called in the dual-core case.

>
> >> Do we need an isync after setting the timebase, to ensure it's happened
> >> before we enable the timebase? Likewise, do we need a readback after
> >> disabling the timebase to ensure it's disabled before we read the
> >> timebase in give_timebase?
> >
> > I checked the e500 core manual (Chapter 2.16 Synchronization Requirements for SPRs).
> > Only some SPR registers need an isync. The timebase registers do not.
>
> I don't trust that, and the consequences of having the sync be imperfect
> are too unpleasant to chance it.
>
> > I did a readback in mpc85xx_timebase_freeze().
>
> Sorry, missed that somehow.
>
> >>> +#ifdef CONFIG_KEXEC
> >>> + np = of_find_matching_node(NULL, guts_ids);
> >>> + if (np) {
> >>> + guts = of_iomap(np, 0);
> >>> + smp_85xx_ops.give_timebase = mpc85xx_give_timebase;
> >>> + smp_85xx_ops.take_timebase = mpc85xx_take_timebase;
> >>> + of_node_put(np);
> >>> + } else {
> >>> + smp_85xx_ops.give_timebase = smp_generic_give_timebase;
> >>> + smp_85xx_ops.take_timebase = smp_generic_take_timebase;
> >>> + }
> >>
> >> Do not use smp_generic_give/take_timebase, ever. If you don't have the
> >> guts node, then just assume the timebase is already synced.
> >>
> >> -Scott
> >
> > smp_generic_give/take_timebase is the default in KEXEC before.
>
> That was a mistake.
>
> > If do not set them, it may make KEXEC fail on other platforms.
>
> What platforms?
>
> -Scott

Such as P4080, P3041, etc.

-Chenhui




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