linux-kernel - Re: [PATCH V1] arm64: dts: qcom: sc7180: Use maximum drive strength values for eMMC

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Date:   Thu, 23 Sep 2021 13:19:37 -0700
From:   Doug Anderson <dianders@...gle.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Asutosh Das <asutoshd@...eaurora.org>,
        Sahitya Tummala <stummala@...eaurora.org>,
        pragalla@...eaurora.org, nitirawa@...eaurora.org,
        Ram Prakash Gupta <rampraka@...eaurora.org>,
        Sayali Lokhande <sayalil@...eaurora.org>,
        sartgarg@...eaurora.org, cang@...eaurora.org,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Andy Gross <agross@...nel.org>,
        Shaik Sajida Bhanu <sbhanu@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH V1] arm64: dts: qcom: sc7180: Use maximum drive strength
 values for eMMC

Bjorn,

On Thu, Aug 19, 2021 at 6:44 AM Doug Anderson <dianders@...gle.com> wrote:
>
> Hi,
>
> On Tue, Aug 17, 2021 at 6:58 AM Doug Anderson <dianders@...gle.com> wrote:
> >
> > >                 pinconf-data {
> > >                         pins = "sdc1_data";
> > >                         bias-pull-up;
> > > -                       drive-strength = <10>;
> > > +                       drive-strength = <16>;
> >
> > I could be convinced that this is the right thing to do, but I want to
> > really make sure that it has had sufficient testing. Specifically as
> > this patch is written we'll be updating the drive strength for all
> > boards. Increasing the drive strength can sometimes introduce new
> > problems (reflections, noise, ...) so we have to be confident that
> > we're not breaking someone that used to work by increasing the drive
> > strength here. How much has this been tested?
>
> From further discussion internally, it sounds as if this should be
> fine and fixes more than just this one eMMC part. Thus:
>
> Reviewed-by: Douglas Anderson <dianders@...omium.org>

We've been running with this patch in the Chrome OS kernel. If it
looks OK to you, it'd be great for it to land in your tree. Thanks!

-Doug