linux-kernel - Re: [PATCH 2/3] arm64: dts: uniphier: add CPU clock and OPP table for LD11 SoC

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Message-ID: <20161019135522.GH11471@vireshk-i7>
Date:   Wed, 19 Oct 2016 19:25:22 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/3] arm64: dts: uniphier: add CPU clock and OPP table
 for LD11 SoC

On 19-10-16, 17:33, Masahiro Yamada wrote:
> Hi Viresh,
> 
> 
> 2016-10-18 20:25 GMT+09:00 Viresh Kumar <viresh.kumar@...aro.org>:
> > On 16-10-16, 23:59, Masahiro Yamada wrote:
> >> +     cluster0_opp: opp_table {
> >> +             compatible = "operating-points-v2";
> >> +             opp-shared;
> >> +
> >> +             opp@...000000 {
> >> +                     opp-hz = /bits/ 64 <245000000>;
> >> +                     clock-latency-ns = <300>;
> >> +             };
> >> +             opp@...000000 {
> >> +                     opp-hz = /bits/ 64 <250000000>;
> >> +                     clock-latency-ns = <300>;
> >> +             };
> >> +             opp@...000000 {
> >> +                     opp-hz = /bits/ 64 <490000000>;
> >> +                     clock-latency-ns = <300>;
> >> +             };
> >> +             opp@...000000 {
> >> +                     opp-hz = /bits/ 64 <500000000>;
> >> +                     clock-latency-ns = <300>;
> >> +             };
> >> +             opp@...333333 {
> >
> > Why isn't ^^ matching with below values ? Same in next patch as well.
> 
> 
> 
> When I try to update /sys/devices/system/cpu/cpufreq/policy*/scaling_max_freq,
> it did not work as I had expected.
> 
> 
> scaling_max_freq is specified by kHz unit,
> on the other hand, clock frequency in the clk driver is specified by Hz.
> 
> 
> 
> If the operating point is 653333kHz, the cpufreq requests
> the clk driver to set 653333000, but it is lower than
> the exact clock, 653333333.
> So, the next lower frequency, 500000000 is selected.
> As a result, the operating point 653333kHz is never enabled.
> 
> 
> So, the operating point must be equal or a little bit bigger.
> 
> 
> Do you know a better way to solve this distortion?

I am not sure about how to fix that problem but there is no reason to
have the exact frequency in opp@*** name. Just use what you have used
in opp-hz line and you will have the exact same behavior.

Right now, its a bit confusing if we read the DT.

-- 
viresh