linux-kernel - Re: [PATCH 5/5] powernv:idle: Disable LOSE_FULL

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Date:   Sat, 8 Jul 2017 19:05:26 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Michael Neuling <mikey@...ling.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH 5/5] powernv:idle: Disable LOSE_FULL_CONTEXT states when
 stop-api fails.

On Fri, 7 Jul 2017 23:07:10 +0530
Gautham R Shenoy <ego@...ux.vnet.ibm.com> wrote:

> 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" <ego@...ux.vnet.ibm.com> wrote:
> >   
> > > From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> > > 
> > > 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.

And POWER8 does not require this?

> 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.

It always restores to deepest stop? Is there any way to restore to the
achieved stop level? Maybe there is no usefulness for that.

Thanks,
Nick