linux-kernel - Re: [PATCH 2/2] powernv: Pass PSSCR value and mask to power9_idle

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Message-ID: <0e7ad8ff-8c44-86bc-f560-258bc7b29a32@gmail.com>
Date:   Tue, 4 Oct 2016 22:33:27 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        "skiboot@...ts.ozlabs.org" <skiboot@...ts.ozlabs.org>
Cc:     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>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH 2/2] powernv: Pass PSSCR value and mask to
 power9_idle_stop



On 04/10/16 21:32, 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.
> 
> That looks good.
> 
>> This patch depends on the following skiboot patch that exports the
>> PSSCR values and the mask for all the stop states:
>> https://lists.ozlabs.org/pipermail/skiboot/2016-September/004869.html
> 
> But we can't depend on a skiboot patch. The kernel has to cope with
> running on an old skiboot.

Hi, Michael

I think with an older skiboot the flags don't get exported and the
new cpuidle (stop state) does not get discovered. I don't think there
is any breakage. Gautham am I missing something?

Balbir Singh.