linux-kernel - Re: [PATCH v5 4/5] powernv: Pass PSSCR value and mask to power9_idle

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Date:   Thu, 12 Jan 2017 22:48:02 +0530
From:   Balbir Singh <bsingharora@...il.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        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, devicetree@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, mark.rutland@....com
Subject: Re: [PATCH v5 4/5] powernv: Pass PSSCR value and mask to
 power9_idle_stop

On Tue, Jan 10, 2017 at 02:37:03PM +0530, Gautham R. Shenoy wrote:
> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> 
> The arch300_idle_stop method currently takes only the requested stop
      power9_idle_stop (see subject :) and second paragraph)
> 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). For the new firmware, the patch will validate that the invariants
> required by the ISA for the psscr values are maintained by the
> firmware.
> 
> This skiboot patch that exports fully populated PSSCR values and the
> mask for all the stop states can be found here:
> https://lists.ozlabs.org/pipermail/skiboot/2016-September/004869.html
> 
> [Optimize the number of instructions before entering STOP with
> ESL=EC=0, validate the PSSCR values provided by the firimware
> maintains the invariants required as per the ISA suggested by Balbir
> Singh]
> 
> Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> ---

Acked-by: Balbir Singh <bsingharora@...il.com>