linux-kernel - Re: [PATCH v6 06/10] dt-bindings: memory-controllers: add Exynos5422 DMC device description

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Message-ID: <CAL_Jsq+bJtjO8xbpnCRHmcyCB=b8DMr73GWKEz+xMXVZag0FrQ@mail.gmail.com>
Date:   Mon, 29 Apr 2019 11:43:38 -0500
From:   Rob Herring <robh@...nel.org>
To:     Lukasz Luba <l.luba@...tner.samsung.com>
Cc:     devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Kukjin Kim <kgene@...nel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kees Cook <keescook@...omium.org>,
        Tony Lindgren <tony@...mide.com>,
        Joerg Roedel <jroedel@...e.de>,
        Thierry Reding <treding@...dia.com>,
        Dmitry Osipenko <digetx@...il.com>, willy.mh.wolff.ml@...il.com
Subject: Re: [PATCH v6 06/10] dt-bindings: memory-controllers: add Exynos5422
 DMC device description

On Mon, Apr 29, 2019 at 7:14 AM Lukasz Luba <l.luba@...tner.samsung.com> wrote:
>
> Hi Rob,
>
> On 4/25/19 9:57 PM, Rob Herring wrote:
> > On Fri, Apr 19, 2019 at 04:19:24PM +0200, Lukasz Luba wrote:
> >> The patch adds description for DT binding for a new Exynos5422 Dynamic
> >> Memory Controller device.
> >>
> >> Signed-off-by: Lukasz Luba <l.luba@...tner.samsung.com>
> >> ---
> >>   .../bindings/memory-controllers/exynos5422-dmc.txt | 73 ++++++++++++++++++++++
> >>   1 file changed, 73 insertions(+)
> >>   create mode 100644 Documentation/devicetree/bindings/memory-controllers/exynos5422-dmc.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/memory-controllers/exynos5422-dmc.txt b/Documentation/devicetree/bindings/memory-controllers/exynos5422-dmc.txt
> >> new file mode 100644
> >> index 0000000..133b3cc
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/memory-controllers/exynos5422-dmc.txt
> >> @@ -0,0 +1,73 @@
> >> +* Exynos5422 frequency and voltage scaling for Dynamic Memory Controller device
> >> +
> >> +The Samsung Exynos5422 SoC has DMC (Dynamic Memory Controller) to which the DRAM
> >> +memory chips are connected. The driver is to monitor the controller in runtime
> >> +and switch frequency and voltage. To monitor the usage of the controller in
> >> +runtime, the driver uses the PPMU (Platform Performance Monitoring Unit), which
> >> +is able to measure the current load of the memory.
> >> +When 'userspace' governor is used for the driver, an application is able to
> >> +switch the DMC and memory frequency.
> >> +
> >> +Required properties for DMC device for Exynos5422:
> >> +- compatible: Should be "samsung,exynos5422-bus".
> >> +- clock-names : the name of clock used by the bus, "bus".
> >> +- clocks : phandles for clock specified in "clock-names" property.
> >> +- devfreq-events : phandles for PPMU devices connected to this DMC.
> >> +- vdd-supply : phandle for voltage regulator which is connected.
> >> +- reg : registers of two CDREX controllers, chip information, clocks subsystem.
> >> +- operating-points-v2 : phandle for OPPs described in v2 definition.
> >> +- device-handle : phandle of the connected DRAM memory device. For more
> >> +    information please refer to Documentation
> >
> > The memory node(s) should be a child of the memory controller IMO.
> I have followed the TI code for LPDDR2. They use 'device-handle'
> probably because the memory controller can be moved into the common
> .dtsi and taken by reference in .dts in a proper board file.

You'd still have to have the ctrlr node in the board file to add the
'device-handle' property.

> The board .dts files might specify different DRAM chips and timings.
> In Exynos case we will also have such situation: one memory controller
> and a few different DRAM chips.

You mean as in the case where there are multiple options and one chip
gets populated on the board? So 'device-handle' is selecting which
chip to use.

You can actually do both here. Keep 'device-handle' to select which
DRAM chip and have the chips as child nodes. But if you really don't
want to have them as child nodes, that's fine.

Rob