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

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Message-ID: <CAJKOXPdoun-2ankrcNzC70tXZi40iONxM3yPstdaiGBMPDjyRQ@mail.gmail.com>
Date:   Tue, 23 Jul 2019 14:08:14 +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 Wed, 17 Jul 2019 at 18:58, Lukasz Luba <l.luba@...tner.samsung.com> wrote:
>
> 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".

Hmm, indeed, you're right. Don't change it then.

Best regards,
Krzysztof