linux-kernel - Re: [PATCH] arm64: dts: qcom: sc7180: Avoid glitching SPI CS at bootup on trogdor

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Date:   Thu, 18 Feb 2021 16:55:33 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Akash Asthana <akashast@...eaurora.org>,
        Andy Gross <agross@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: qcom: sc7180: Avoid glitching SPI CS at
 bootup on trogdor

Hi,

On Thu, Feb 18, 2021 at 2:55 PM Douglas Anderson <dianders@...omium.org> wrote:
>
> it's believed
> that, under certain timing conditions, it could be getting the EC into
> a confused state causing the EC driver to fail to probe.

Believed => confirmed

I _think_ <https://issuetracker.google.com/180655198> is public.  It
explains why this was causing the EC driver to fail to prove.  In
short: it turns out that when we glitched the EC it printed to its
console.  If the EC's uptime was long enough then it would spend
enough time printing the timestamp for this error message (a bunch of
64-bit divide by 10) that it wouldn't be ready for the message we sent
to it.  Doh!

-Doug