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

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Date:   Wed, 17 Jul 2019 18:58:11 +0200
From:   Lukasz Luba <l.luba@...tner.samsung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
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

Hi Krzysztof,

On 7/17/19 12:15 PM, Krzysztof Kozlowski wrote:
> 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/
please see below
> 
>> 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/
Actually, I have double checked that, because we always used this 
terminology: low OPP, high OPP, lower OPPs, higher OPPs. I can change
it here for you, but I think this is not something that people are used
to. Please check EAS pdf documentation or this file:
https://www.kernel.org/doc/Documentation/scheduler/sched-energy.txt
i.e. "running at a lower OPP" or "high OPPs", "lowest OPPs".

Regards,
Lukasz
> 
>> 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
>>
> 
>