linux-kernel - Re: [PATCH 5/8] arm64: dts: tegra186: Add SDMMC4 DQS trim value

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Date:   Thu, 9 Aug 2018 08:23:16 -0400
From:   Peter Geis <pgwipeout@...il.com>
To:     Aapo Vienamo <avienamo@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] arm64: dts: tegra186: Add SDMMC4 DQS trim value



On 08/09/2018 08:02 AM, Aapo Vienamo wrote:
> On Thu, 9 Aug 2018 13:49:22 +0200
> Thierry Reding <thierry.reding@...il.com> wrote:
> 
>> On Tue, Aug 07, 2018 at 05:00:01PM +0300, Aapo Vienamo wrote:
>>> Add the HS400 DQS trim value for Tegra186 SDMMC4.
>>>
>>> Signed-off-by: Aapo Vienamo <avienamo@...dia.com>
>>> ---
>>>   arch/arm64/boot/dts/nvidia/tegra186.dtsi | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/arch/arm64/boot/dts/nvidia/tegra186.dtsi b/arch/arm64/boot/dts/nvidia/tegra186.dtsi
>>> index 6e9ef26..9e07bc6 100644
>>> --- a/arch/arm64/boot/dts/nvidia/tegra186.dtsi
>>> +++ b/arch/arm64/boot/dts/nvidia/tegra186.dtsi
>>> @@ -313,6 +313,7 @@
>>>   		nvidia,pad-autocal-pull-down-offset-1v8-timeout = <0x0a>;
>>>   		nvidia,default-tap = <0x5>;
>>>   		nvidia,default-trim = <0x9>;
>>> +		nvidia,dqs-trim = <63>;
>>>   		status = "disabled";
>>>   	};
>>>     
>>
>> Isn't this technically dependent on the board layout and as such would
>> belong in the board DTS file? Or does this value work on all existing
>> Tegra186 platforms?
> 
> This value is specified as part of the controller initialization
> sequence in the TRM. I've understood that this (and other tap and trim)
> value(s) are used for compensating the propagation delay differences
> that are caused by the internal SoC layout.
> 
>   -Aapo
> --

The Tegra2 and Tegra3 TRMs also specify recommended DQS values, and I am 
working on at least one device that differs in the platform data from 
the default value.
I see that you mentioned this is for the newer devices that support 
HS200/HS400 modes, but does it enable setting DQS on older devices?