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

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Message-ID: <7b6867f4-54b2-f3b5-2b4e-87ea3000fa44@gmail.com>
Date:   Thu, 2 May 2019 04:39:44 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Rob Herring <robh@...nel.org>
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

02.05.2019 3:52, Dmitry Osipenko пишет:
> 02.05.2019 3:17, Rob Herring пишет:
>> 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?
> 
> Because this is not a standard PC, but a custom embedded hardware that
> is simpler and also doesn't fully follow the standards in some cases.

Even if there is a way to derive at least some of required parameters
from the common timing, I don't have information about how to do it and
there is pretty much no chance to get it into public.

Rob, please let me know if you're okay with this binding.