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

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Date:   Thu, 9 Aug 2018 15:37:32 +0300
From:   Aapo Vienamo <avienamo@...dia.com>
To:     Peter Geis <pgwipeout@...il.com>
CC:     Thierry Reding <thierry.reding@...il.com>,
        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 Thu, 9 Aug 2018 08:23:16 -0400
Peter Geis <pgwipeout@...il.com> wrote:

> 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?

I can't find any mention of _SDMMC_ DQS trimmer on Tegra2, Tegra3 or
Tegra124 TRMs. As far as I can tell, programming the DQS trimmer value
is only required by HS400 signaling on Tegra210 and Tegra186.

 -Aapo