linux-kernel - Re: [PATCH v3 3/3] powernv: Pass PSSCR value and mask to power9_idle

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Date:   Tue, 29 Nov 2016 11:40:35 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Michael Neuling <mikey@...ling.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        "Shreyas B. Prabhu" <shreyasbp@...il.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        "Oliver O'Halloran" <oohall@...il.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, skiboot@...ts.ozlabs.org
Subject: Re: [PATCH v3 3/3] powernv: Pass PSSCR value and mask to
 power9_idle_stop

Hi Michael,

On Wed, Nov 23, 2016 at 08:51:10PM +1100, Michael Ellerman wrote:
> "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com> writes:
> 
> > From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> >
> > The power9_idle_stop method currently takes only the requested stop
> > level as a parameter and picks up the rest of the PSSCR bits from a
> > hand-coded macro. This is not a very flexible design, especially when
> > the firmware has the capability to communicate the psscr value and the
> > mask associated with a particular stop state via device tree.
> >
> > This patch modifies the power9_idle_stop API to take as parameters the
> > PSSCR value and the PSSCR mask corresponding to the stop state that
> > needs to be set. These PSSCR value and mask are respectively obtained
> > by parsing the "ibm,cpu-idle-state-psscr" and
> > "ibm,cpu-idle-state-psscr-mask" fields from the device tree.
> >
> > In addition to this, the patch adds support for handling stop states
> > for which ESL and EC bits in the PSSCR are zero. As per the
> > architecture, a wakeup from these stop states resumes execution from
> > the subsequent instruction as opposed to waking up at the System
> > Vector.
> >
> > The older firmware sets only the Requested Level (RL) field in the
> > psscr and psscr-mask exposed in the device tree. For older firmware
> > where psscr-mask=0xf, this patch will set the default sane values that
> > the set for for remaining PSSCR fields (i.e PSLL, MTL, ESL, EC, and
> > TR).
> 
> So we're using psscr-mas=0xf as a signal that we're running on old
> firmware.
> 
> That's OK I think, but please send a patch to document it in the device
> tree binding.
> 
> And call it out below in the code.

Sure will do this! Thanks for reviewing the code.

> 
> cheers
> 

--
Thanks and Regards
gautham.