linux-kernel - Re: [PATCH v7 07/13] dt-bindings: memory-controllers: add Exynos5422 DMC device description

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Message-ID: <CAJKOXPc2Swoi+xc_=QTMdY8p2DTtf5SprpfMFC6B9QCNUtxm-w@mail.gmail.com>
Date:   Wed, 8 May 2019 12:19:04 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Lukasz Luba <l.luba@...tner.samsung.com>
Cc:     Rob Herring <robh@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        Bartłomiej Żołnierkiewicz 
        <b.zolnierkie@...sung.com>, kgene@...nel.org,
        Chanwoo Choi <cw00.choi@...sung.com>,
        kyungmin.park@...sung.com,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        s.nawrocki@...sung.com, myungjoo.ham@...sung.com,
        keescook@...omium.org, tony@...mide.com, jroedel@...e.de,
        treding@...dia.com, digetx@...il.com, willy.mh.wolff.ml@...il.com
Subject: Re: [PATCH v7 07/13] dt-bindings: memory-controllers: add Exynos5422
 DMC device description

On Wed, 8 May 2019 at 11:45, Lukasz Luba <l.luba@...tner.samsung.com> wrote:
>
>
> On 5/8/19 9:19 AM, Krzysztof Kozlowski wrote:
> > On Tue, 7 May 2019 at 19:04, Rob Herring <robh@...nel.org> wrote:
> >>> +- devfreq-events : phandles of the PPMU events used by the controller.
> >>> +- samsung,syscon-chipid : phandle of the ChipID used by the controller.
> >>> +- samsung,syscon-clk : phandle of the clock register set used by the controller.
> >>
> >> Looks like a hack. Can't you get this from the clocks property? What is
> >> this for?
> >
> > Hi Rob,
> >
> > Lukasz uses these two syscon regmaps to read certain registers. For
> > chipid he reads it to check the size of attached memory (only 2 GB
> > version is supported). This indeed looks like a hack. However the
> > second regmap (clk) is needed to get the timing data from registers
> > from DMC clock driver address space. These are registers with memory
> > timing so their data is not exposed anyway in common clk framework.
> >
> > Best regards,
> > Krzysztof
>
> Thank you Krzysztof for a fast response. I have also responded to Rob.
> I wouldn't call accessing chipid registers as a hack, though. The DMC
> registers do not contain information about the memory chip since it is
> in phase of production the board not the chip. Thus, chipid regs (which
> loads from e-fuses) are best place to put information about memory
> type/size.

By hack I meant that you have to read chipid instead of DTS... but as
you pointed, the DTS could not match the real fused values so actually
it makes sense to read them.

Best regards,
Krzysztof