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From: Balbir Singh <bsingharora@gmail.com>
Date: Sun, 17 Dec 2017 14:15:25 +1100
Message-ID: <CAKTCnz=jrvbizrzUx1tDxMg__4coJHoxSXOS+K+zXQVAM=WF-g@mail.gmail.com>
Subject: Re: [v3 PATCH 2/3] powernv-cpufreq: Fix pstate_to_idx() to handle
 non-continguous pstates
To: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
Cc: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, huntbag@linux.vnet.ibm.com,
        Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
        linux-pm@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@lists.ozlabs.org>
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On Wed, Dec 13, 2017 at 5:57 PM, Gautham R. Shenoy
<ego@linux.vnet.ibm.com> wrote:
> From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
>
> The code in powernv-cpufreq, makes the following two assumptions which
> are not guaranteed by the device-tree bindings:
>
>     1) Pstate ids are continguous: This is used in pstate_to_idx() to
>        obtain the reverse map from a pstate to it's corresponding
>        entry into the cpufreq frequency table.
>
>     2) Every Pstate should always lie between the max and the min
>        pstates that are explicitly reported in the device tree: This
>        is used to determine whether a pstate reported by the PMSR is
>        out of bounds.
>
> Both these assumptions are unwarranted and can change on future
> platforms.

While this is a good thing, I wonder if it is worth the complexity. Pstates
are contiguous because they define transitions in incremental value
of change in frequency and I can't see how this can be broken in the
future?

Balbir Singh.