linux-kernel - Re: [PATCH v1 37/50] ARM: dts: exynos: change parent and rate of bus

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Date:   Wed, 17 Jul 2019 12:45:12 +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 37/50] ARM: dts: exynos: change parent and rate of
 bus_fsys in Exynos5422

On Wed, 17 Jul 2019 at 12:39, Lukasz Luba <l.luba@...tner.samsung.com> wrote:
> >>
> >>   &bus_fsys {
> >>          devfreq = <&bus_wcore>;
> >> +       assigned-clocks = <&clock CLK_MOUT_ACLK200_FSYS>,
> >> +                         <&clock CLK_DOUT_ACLK200_FSYS>,
> >> +                         <&clock CLK_FOUT_DPLL>;
> >> +       assigned-clock-parents = <&clock CLK_MOUT_SCLK_DPLL>;
> >> +       assigned-clock-rates = <0>, <240000000>,<1200000000>;
> >
> > Here and in all other patches:
> > I am not entirely sure that this should be here. It looks like
> > property of the SoC. Do we expect that buses will be configured to
> > different clock rates between different boards? Since the OPP tables
> > are shared (they are property of the SoC, not board) then I would
> > assume that default frequency is shared as well.
> These clocks they all relay on some bootloader configuration. It depends
> which version of the bootloader you have, then you might get different
> default configuration in the clocks.

I do not agree here. This configuration is not dependent on
bootloader. Although one bootloader might set the clocks to X and
other to Y, but still you provide here valid configuration setting
them, e.g. to Y (or to Z). What bootloader set before does not matter
because you always override it.

> The pattern of changing the parent
> or even rate is known in the DT files (or I am missing something).
> When you grep for it, you get 168 hits (38 for exynos*):
> git grep -n "assigned-clock-rates" ./arch/arm/boot/dts/ | wc -l

Yeah, and if you grep per type you got:
DTSI: 114
DTS: 54
so what do you want to say?

My thinking is that all the boards have buses configured to the same
initial frequency. I am not questioning the use of
assigned-clock-rates at all. Just the place...

BR,
Krzysztof