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

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Date:   Tue, 25 May 2021 17:48:16 +0800
From:   Steven Lee <steven_lee@...eedtech.com>
To:     Joel Stanley <joel@....id.au>
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

The 05/25/2021 15:55, Joel Stanley wrote:
> On Mon, 24 May 2021 at 07:33, Steven Lee <steven_lee@...eedtech.com> wrote:
> >
> > AST2600-A2 EVB has the reference design for enabling SD bus
> > power and toggling SD bus signal voltage between 3.3v and 1.8v by
> > GPIO regulators.
> > This patch series adds sdhci node and gpio regulators in a new dts file
> > for AST2600-A2 EVB.
> > The description of the reference design of AST2600-A2 EVB is added
> > in the new dts file.
> >
> > This patch also include a helper for updating AST2600 sdhci capability
> > registers.
> 
> The device trees look good:
> 
> Reviewed-by: Joel Stanley <joel@....id.au>
> 
> I've applied patches 1-3 to the aspeed tree for v5.14. I made a little
> fix to patch 3 as it needed to add the new device tree to the
> makefile.
> 

Thanks!

> 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.

> Cheers,
> 
> Joel