linux-kernel - Re: [PATCH v5 0/4] mmc: sdhci-of-aspeed: Support toggling SD bus signal

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Message-ID: <CACPK8XfdYAcx=RX07hf1ar8A7th8G8390exvKbgh92X=ov8u2A@mail.gmail.com>
Date:   Tue, 25 May 2021 12:56:03 +0000
From:   Joel Stanley <joel@....id.au>
To:     Steven Lee <steven_lee@...eedtech.com>
Cc:     Andrew Jeffery <andrew@...id.au>, Rob Herring <robh+dt@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:ARM/ASPEED MACHINE SUPPORT" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/ASPEED MACHINE SUPPORT" 
        <linux-aspeed@...ts.ozlabs.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "moderated list:ASPEED SD/MMC DRIVER" <openbmc@...ts.ozlabs.org>,
        Hongwei Zhang <Hongweiz@....com>,
        Ryan Chen <ryan_chen@...eedtech.com>,
        Chin-Ting Kuo <chin-ting_kuo@...eedtech.com>
Subject: Re: [PATCH v5 0/4] mmc: sdhci-of-aspeed: Support toggling SD bus signal

On Tue, 25 May 2021 at 09:48, Steven Lee <steven_lee@...eedtech.com> wrote:
>
> The 05/25/2021 15:55, Joel Stanley wrote:
> > When I was testing on my A2 EVB I saw this:
> >
> > [    1.436219] sdhci-aspeed 1e750100.sdhci: Requested out of range
> > phase tap 192 for 9 degrees of phase compensation at 1562500Hz,
> > clamping to tap 15
> > [    1.450913] sdhci-aspeed 1e750100.sdhci: Requested out of range
> > phase tap 963 for 45 degrees of phase compensation at 1562500Hz,
> > clamping to tap 15
> >
> > Do you know what is happening there?
> >
>
> Per MMC spec, eMMC bus speed is set as legacy mode(0~26MHz) at startup of
> eMMC initializtion flow. Clock phase calculation is triggered in set_clock()
> and it calculates taps based on phase_deg(<9>, <225>) in the dts file and the
> current speed(1562500Hz), which causes the warning message you mentioned.
> As the phase_deg in the dts file should be calculated with 100MHz.
>
> https://lkml.org/lkml/2021/5/24/95
>
> But after some initialization flow, eMMC bus speed will be set to
> correct speed(100MHz).
> Clock phase calculation will be triggered again to get correct taps.

Thanks for the explanation. I added another debug print and I can see
it doing what you describe:

[    1.465904] sdhci-aspeed 1e750100.sdhci: Requested out of range
phase tap 192 for 9 degrees of phase compensation at 1562500Hz,
clamping to tap 15
[    1.480598] sdhci-aspeed 1e750100.sdhci: rate 1562500 phase 9 tap 15
[    1.490316] sdhci-aspeed 1e750100.sdhci: Requested out of range
phase tap 963 for 45 degrees of phase compensation at 1562500Hz,
clamping to tap 15
[    1.505077] sdhci-aspeed 1e750100.sdhci: rate 1562500 phase 45 tap 15
[    1.515059] sdhci-aspeed 1e750100.sdhci: rate 100000000 phase 9 tap 3
[    1.524886] sdhci-aspeed 1e750100.sdhci: rate 100000000 phase 45 tap 15
[    1.534904] sdhci-aspeed 1e750100.sdhci: rate 100000000 phase 9 tap 3
[    1.544713] sdhci-aspeed 1e750100.sdhci: rate 100000000 phase 45 tap 15

We should change the "out of range" message to be dev_dbg, as it is
expected on a normal boot.

Cheers,

Joel