linux-kernel - Re: [PATCH 3/3] powernv:idle: Set LPCR

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Date:   Thu, 13 Apr 2017 17:24:34 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Michael Neuling <mikey@...ling.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Shreyas B. Prabhu" <shreyasbp@...il.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Anton Blanchard <anton@...ba.org>,
        Balbir Singh <bsingharora@...il.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        Mahesh J Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] powernv:idle: Set LPCR_UPRT on wakeup from deep-stop

On Thu, Apr 13, 2017 at 05:18:17PM +1000, Nicholas Piggin wrote:
> On Thu, 13 Apr 2017 16:27:34 +1000
> Michael Neuling <mikey@...ling.org> wrote:
> 
> > On Thu, 2017-04-13 at 14:12 +1000, Benjamin Herrenschmidt wrote:
> > > On Thu, 2017-04-13 at 09:28 +0530, Aneesh Kumar K.V wrote:  
> > > > >   #endif
> > > > >        mtctr   r12
> > > > >        bctrl
> > > > > +/*
> > > > > + * cur_cpu_spec->cpu_restore would restore LPCR to a
> > > > > + * sane value that is set at early boot time,
> > > > > + * thereby clearing LPCR_UPRT.
> > > > > + * LPCR_UPRT is required if we are running in Radix mode.
> > > > > + * Set it here if that be the case.
> > > > > + */
> > > > > +BEGIN_MMU_FTR_SECTION
> > > > > +     mfspr   r3, SPRN_LPCR
> > > > > +     LOAD_REG_IMMEDIATE(r4, LPCR_UPRT)
> > > > > +     or      r3, r3, r4
> > > > > +     mtspr   SPRN_LPCR, r3
> > > > > +END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)  
> > > 
> > > We are probably better off saving the value somewhere during boot
> > > and just "blasting" it whole back.  
> > 
> > We seem to touch LPCR in a bunch of places these days.  Not sure when "sometimes
> >  during boot" should actually be.
> 
> In the short term, what if we just save LPCR and restore it after calling
> cpu_restore? As you say there are a lot of things that touch LPCR we're
> not catching here.

In that case can we skip calling cpu_restore in the idle_exit path
altogether and simply restore LPCR to the value that the thread had
before executing stop ?

> 

--
Thanks and Regards
gautham.