linux-kernel - Re: [PATCH v1 27/50] ARM: dts: exynos: align bus

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Date:   Wed, 17 Jul 2019 12:15:37 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Lukasz Luba <l.luba@...tner.samsung.com>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>, linux-clk@...r.kernel.org,
        mturquette@...libre.com, sboyd@...nel.org,
        Bartłomiej Żołnierkiewicz 
        <b.zolnierkie@...sung.com>, kgene@...nel.org, mark.rutland@....com,
        robh+dt@...nel.org, Chanwoo Choi <cw00.choi@...sung.com>,
        kyungmin.park@...sung.com, Andrzej Hajda <a.hajda@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        s.nawrocki@...sung.com, myungjoo.ham@...sung.com
Subject: Re: [PATCH v1 27/50] ARM: dts: exynos: align bus_wcore OPPs in Exynos5420

On Mon, 15 Jul 2019 at 14:44, Lukasz Luba <l.luba@...tner.samsung.com> wrote:
>
> This is the most important bus in the Exynos5x SoC. The whole communication
> inside SoC does through that bus (apart from direct requests from CCI to
> DRAM controller). It is also modeled as a master bus in devfreq framework.
> It is also the only one OPP table throughout other buses which has voltage
> values. The devfreq software controls the speed of that bus and other
> buses. The other buses follows the rate of the master. There is only one
> regulator. The old lowest OPP had pair 925mV, 84MHz which is enough for

s/lowest/slowest/

> this frequency. However, due to the fact that the other buses follows the
> WCORE bus by taking the OPP from their table with the same id, e.g. opp02,
> the children frequency should be stable with the set voltage.
> It could cause random faults very hard to debug.
> Thus, the patch removes the lowest OPP to make other buses' lowest OPPs

s/lowest/slowest/

> working. The new lowest OPP has voltage high enough for buses working up
> to 333MHz. It also changes the frequencies of the OPPs to align them to
> PLL value such that it is possible to set them using only a divider without
> reprogramming OPP.

Reprogramming OPP? What is it?

> Reprogramming the PLL was not set, so the real frequency

I understood from the previous that reprogramming the OPP (PLL?) was
happening... Please rephrase entire sentence.

BR,
Krzysztof

> values were not the one from the OPP table, which could confuse the
> governor algorithms which relay on OPP speed values making the system to
> behave weird.
>
> Signed-off-by: Lukasz Luba <l.luba@...tner.samsung.com>
> ---
>  arch/arm/boot/dts/exynos5420.dtsi | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm/boot/dts/exynos5420.dtsi b/arch/arm/boot/dts/exynos5420.dtsi
> index f8c36ff0d4c3..a355c76af5a5 100644
> --- a/arch/arm/boot/dts/exynos5420.dtsi
> +++ b/arch/arm/boot/dts/exynos5420.dtsi
> @@ -1107,22 +1107,18 @@
>                         compatible = "operating-points-v2";
>
>                         opp00 {
> -                               opp-hz = /bits/ 64 <84000000>;
> -                               opp-microvolt = <925000>;
> +                               opp-hz = /bits/ 64 <150000000>;
> +                               opp-microvolt = <950000>;
>                         };
>                         opp01 {
> -                               opp-hz = /bits/ 64 <111000000>;
> +                               opp-hz = /bits/ 64 <200000000>;
>                                 opp-microvolt = <950000>;
>                         };
>                         opp02 {
> -                               opp-hz = /bits/ 64 <222000000>;
> +                               opp-hz = /bits/ 64 <300000000>;
>                                 opp-microvolt = <950000>;
>                         };
>                         opp03 {
> -                               opp-hz = /bits/ 64 <333000000>;
> -                               opp-microvolt = <950000>;
> -                       };
> -                       opp04 {
>                                 opp-hz = /bits/ 64 <400000000>;
>                                 opp-microvolt = <987500>;
>                         };
> --
> 2.17.1
>