Re: [XenPPC] [PATCH] Disable DPM until code is audited

[Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>]

> > > Most JS20 and JS21 have DPM disabled on the board,
> > What does this mean?  SLOF/js2x enables DPM always, for
> > example; there is no hardware override that I'm aware of.
> According to S9.9 of 970FX UM:
>   Dynamic power management can be disabled in the RAS units by  
> asserting bit[0]
>   in the JTAG register with modifier address 0x000800.
Oh okay, that's not a *hardware* disable.  Well could be that
it's enabled on JS2x, I dunno.

> > > which is why we have not seen any SMP problems with them.   
> > > However the Maple-D and the JS20 model Amos cites both have had  
> > > problems with the one of these two modes.  That model seems to be  
> > > the newest JS20 we've run on.
> > Sounds like the problem manifests itself on all 970FX and
> > no other CPUs from the 970 family.
> I was under the impression that we had other 970FX js20s but  
> perhaps we do not
The 2.2GHz ones are 970FX, the 1.6GHz ones are not.

> > My question remains: did you try with NAP disabled and
> > DPM enabled?
> I see, so:
>   HID0[NAP]=1
>   HID0[DPM]=1
>   MSR[POW]=1
>
> is NAP and is different than:
>   HID0[NAP]=0
>   HID0[DPM]=1
>   MSR[POW]=1
> which is something else?
NAP=0 DPM=1 POW=whatever is what I was after.

DPM is not a power-down mode; it's just (fine-grained) clock
gating AFAIK, it shouldn't make anything slower ever.

> Sure I'll try that.
Thanks!


Segher


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