linux-kernel - Re: [PATCH 1/8] dt-bindings: mmc: Add DQS trim value to Tegra SDHCI

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Message-ID: <20180809140948.GI21639@ulmo>
Date:   Thu, 9 Aug 2018 16:09:48 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Aapo Vienamo <avienamo@...dia.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 1/8] dt-bindings: mmc: Add DQS trim value to Tegra SDHCI

On Thu, Aug 09, 2018 at 05:06:04PM +0300, Aapo Vienamo wrote:
> On Thu, 9 Aug 2018 15:46:48 +0200
> Thierry Reding <thierry.reding@...il.com> wrote:
> 
> > On Thu, Aug 09, 2018 at 02:45:15PM +0300, Aapo Vienamo wrote:
> > > On Thu, 9 Aug 2018 13:36:09 +0200
> > > Thierry Reding <thierry.reding@...il.com> wrote:
> > >   
> > > > On Tue, Aug 07, 2018 at 04:59:57PM +0300, Aapo Vienamo wrote:  
> > > > > Document HS400 DQS trim value device tree property.
> > > > > 
> > > > > Signed-off-by: Aapo Vienamo <avienamo@...dia.com>
> > > > > ---
> > > > >  Documentation/devicetree/bindings/mmc/nvidia,tegra20-sdhci.txt | 3 +++
> > > > >  1 file changed, 3 insertions(+)
> > > > > 
> > > > > diff --git a/Documentation/devicetree/bindings/mmc/nvidia,tegra20-sdhci.txt b/Documentation/devicetree/bindings/mmc/nvidia,tegra20-sdhci.txt
> > > > > index 3c7960a..7d294f3 100644
> > > > > --- a/Documentation/devicetree/bindings/mmc/nvidia,tegra20-sdhci.txt
> > > > > +++ b/Documentation/devicetree/bindings/mmc/nvidia,tegra20-sdhci.txt
> > > > > @@ -72,6 +72,7 @@ Optional properties for Tegra210 and Tegra186:
> > > > >    trimmer value for non-tunable modes.
> > > > >  - nvidia,default-trim : Specify the default outbound clock trimmer
> > > > >    value.
> > > > > +- nvidia,dqs-trim : Specify DQS trim value for HS400 timing
> > > > >  
> > > > >    Notes on the pad calibration pull up and pulldown offset values:
> > > > >      - The property values are drive codes which are programmed into the
> > > > > @@ -88,6 +89,8 @@ Optional properties for Tegra210 and Tegra186:
> > > > >      - The values are programmed to the Vendor Clock Control Register.
> > > > >        Please refer to the reference manual of the SoC for correct
> > > > >        values.
> > > > > +    - The DQS trim values are only used on controllers which support
> > > > > +      HS400 timing.    
> > > > 
> > > > One of these additions says "DQS trim values", the other says "DQS trim
> > > > value". It is unclear from the above how many values there are. I think
> > > > this should be more explicit. Also, I don't see why the note about which
> > > > controllers the DQS trim value(s) applies to is in a separate paragraph.
> > > > Couldn't it be moved to the property description?  
> > > 
> > > It's a single value. The plural form is a mistake.
> > >   
> > > > Also, I think the bindings should specify which generations of Tegra do
> > > > support HS400. Where else are people supposed to find that information?  
> > > 
> > > This property is under the "Optional properties for Tegra210 and
> > > Tegra186" section and it only applies for the said generations.  
> > 
> > What's the point of specifying that they are only used on controllers
> > which support HS400? Are you saying that only a subset of the SDHCI
> > controllers on Tegra210 and Tegra186 support HS400?
> 
> Yes, on Tegra210 and Tegra186 only SDMMC4 supports HS400.

Good. I think that'd be good to have as part of the DT bindings
documentation.

Thierry

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