Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
User-Agent: Cyrus-JMAP/3.5.0-alpha0-448-gae190416c7-fm-20210505.004-gae190416
Mime-Version: 1.0
Message-Id: <e95c5263-d50f-4316-bb93-e14449559b1b@www.fastmail.com>
In-Reply-To: <CACPK8XfdYAcx=RX07hf1ar8A7th8G8390exvKbgh92X=ov8u2A@mail.gmail.com>
References: <20210524073308.9328-1-steven_lee@aspeedtech.com>
 <CACPK8XcfvUQD5xwb=2Va5Sr+bmaWfJMZkh61HK1=J1qLYc84zQ@mail.gmail.com>
 <20210525094815.GA8757@aspeedtech.com>
 <CACPK8XfdYAcx=RX07hf1ar8A7th8G8390exvKbgh92X=ov8u2A@mail.gmail.com>
Date:   Wed, 26 May 2021 08:29:41 +0930
From:   "Andrew Jeffery" <andrew@aj.id.au>
To:     "Joel Stanley" <joel@jms.id.au>,
        "Steven Lee" <steven_lee@aspeedtech.com>
Cc:     "Rob Herring" <robh+dt@kernel.org>,
        "Adrian Hunter" <adrian.hunter@intel.com>,
        "Ulf Hansson" <ulf.hansson@linaro.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        "moderated list:ARM/ASPEED MACHINE SUPPORT" 
        <linux-arm-kernel@lists.infradead.org>,
        "moderated list:ARM/ASPEED MACHINE SUPPORT" 
        <linux-aspeed@lists.ozlabs.org>,
        "open list" <linux-kernel@vger.kernel.org>,
        linux-mmc <linux-mmc@vger.kernel.org>,
        "moderated list:ASPEED SD/MMC DRIVER" <openbmc@lists.ozlabs.org>,
        "Hongwei Zhang" <Hongweiz@ami.com>,
        "Ryan Chen" <ryan_chen@aspeedtech.com>,
        "Chin-Ting Kuo" <chin-ting_kuo@aspeedtech.com>
Subject: =?UTF-8?Q?Re:_[PATCH_v5_0/4]_mmc:_sdhci-of-aspeed:_Support_toggling_SD_b?=
 =?UTF-8?Q?us_signal?=
Content-Type: text/plain
Precedence: bulk


On Tue, 25 May 2021, at 22:26, Joel Stanley wrote:
> On Tue, 25 May 2021 at 09:48, Steven Lee <steven_lee@aspeedtech.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.

I would think the issue is rather that we shouldn't be applying a phase 
correction for a bus speed that isn't what the correction was specified 
for.

Let me look at this a bit further.

Andrew