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

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Date:   Wed, 8 May 2019 11:45:29 +0200
From:   Lukasz Luba <l.luba@...tner.samsung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        Rob Herring <robh@...nel.org>
Cc:     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 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.

Regards,
Lukasz