Re: [PATCH v2 2/3] powerpc/powernv/idle: save-restore DAWR0, DAWRX0 for P10

[Ravi Bangoria]

Hi Nick,

On 7/13/20 11:22 AM, Nicholas Piggin wrote:
> Excerpts from Pratik Rajesh Sampat's message of July 10, 2020 3:22 pm:
> > Additional registers DAWR0, DAWRX0 may be lost on Power 10 for
> > stop levels < 4.
> > Therefore save the values of these SPRs before entering a  "stop"
> > state and restore their values on wakeup.
>
> Hmm, where do you get this from? Documentation I see says DAWR is lost
> on POWER9 but not P10.
>
> Does idle thread even need to save DAWR, or does it get switched when
> going to a thread that has a watchpoint set?

I don't know how idle states works internally but IIUC, we need to save/restore
DAWRs. This is needed when user creates per-cpu watchpoint event.

Ravi