linux-kernel - Re: [PATCH v2 2/4] dt-bindings: memory: Add binding for NVIDIA Tegra30 External Memory Controller

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Message-ID: <CAL_JsqKCWytgQEDPLX27xdaDrARtHssbhFcL47RO0zfECm0Gig@mail.gmail.com>
Date:   Wed, 1 May 2019 19:17:03 -0500
From:   Rob Herring <robh@...nel.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Joseph Lo <josephl@...dia.com>, devicetree@...r.kernel.org,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-tegra@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] dt-bindings: memory: Add binding for NVIDIA
 Tegra30 External Memory Controller

On Wed, May 1, 2019 at 7:06 PM Dmitry Osipenko <digetx@...il.com> wrote:
>
> 30.04.2019 1:05, Rob Herring пишет:
> > On Sun, Apr 14, 2019 at 11:20:07PM +0300, Dmitry Osipenko wrote:
> >> Add device-tree binding for NVIDIA Tegra30 External Memory Controller.
> >> The binding is based on the Tegra124 EMC binding since hardware is
> >> similar, although there are couple significant differences.
> >
> > My comments on Tegra124 binding apply here.
>
> The common timing definition doesn't fully match the definition that is
> used by Tegra's Memory Controller, thus the DQS (data strobe) timing
> parameter is comprised of multiple sub-parameters that describe how to
> generate the strobe in hardware. There are also more additional
> parameters that are specific to Tegra and they are individually
> characterized for each memory model and clock rate. Hence the common
> timing definition isn't usable.

I don't understand. Every PC in the world can work with any DIMM
(within a given generation) just with SPD data. Why is that not
sufficient here?

In any case, it seems for Tegra124 a different approach is going to be
taken. Seems like an "avoid DT" solution to me, but if it's contained
within the firmware it's not my problem.

Rob