Subject: Re: [PATCH 5/5] powernv:idle: Disable LOSE_FULL_CONTEXT states when stop-api fails.

From: Gautham R Shenoy <[email-masked]>
Date: Fri, 7 Jul 2017 23:07:10 +0530

On Fri, Jul 07, 2017 at 01:29:16AM +1000, Nicholas Piggin wrote:
> On Wed,  5 Jul 2017 22:08:16 +0530
> "Gautham R. Shenoy" <[email-masked]> wrote:
> 
> > From: "Gautham R. Shenoy" <[email-masked]>
> > 
> > Currently, we use the opal call opal_slw_set_reg() to inform the that
> > the Sleep-Winkle Engine (SLW) to restore the contents of some of the
> > Hypervisor state on wakeup from deep idle states that lose full
> > hypervisor context (characterized by the flag
> > OPAL_PM_LOSE_FULL_CONTEXT).
> > 
> > However, the current code has a bug in that if opal_slw_set_reg()
> > fails, we don't disable the use of these deep states (winkle on
> > POWER8, stop4 onwards on POWER9).
> > 
> > This patch fixes this bug by ensuring that if the the sleep winkle
> > engine is unable to restore the hypervisor states in
> > pnv_save_sprs_for_deep_states(), then we mark as invalid the states
> > which lose full context.
> > 
> > As a side-effect, since supported_cpuidle_states in
> > pnv_probe_idle_states() consists of flags of only the valid states,
> > this patch will ensure that no other subsystem in the kernel can use
> > the states which lose full context on stop-api failures.
> 
> Looks good. Is there something minimal we can do for stable here?
> 
> Aside question, do we need to restore LPCR at all with the SLW engine?
> It gets set up again when by the idle wakeup code.

> 
> And does POWER9 really need MSR and PSSCR restored by SLW? (going a bit
> off topic here, I'm just curious)

MSR is needed to be restored so that we wakeup with the right
endianness and with the IR,DR disabled.

PSSCR is set to a value so that in case of a special wakeup for a
deep-stop, the SLW can program the core to go back to the stop level
provided by the PSSCR value via the stop-api.

> Thanks,
> Nick

--
Thanks and Regards
gautham.