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

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Date:   Thu, 9 Aug 2018 08:50:05 -0400
From:   Peter Geis <pgwipeout@...il.com>
To:     Aapo Vienamo <avienamo@...dia.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 08/09/2018 08:37 AM, Aapo Vienamo wrote:
> 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
> 
Apologies, I was referring to the default Tap/Trim values.
DQS found it's way into my brain from the memory controller.