linux-kernel - Re: [PATCH 1/2] clk: qcom: gcc-sc7180: Use floor ops for sdcc clks

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Date:   Thu, 10 Dec 2020 13:00:45 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Taniya Das <tdas@...eaurora.org>,
        Veerabhadrarao Badiganti <vbadigan@...eaurora.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] clk: qcom: gcc-sc7180: Use floor ops for sdcc clks

Hi,

On Thu, Dec 10, 2020 at 12:27 PM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Quoting Douglas Anderson (2020-12-10 10:22:38)
> > I would repeat the same commit message that was in commit 5e4b7e82d497
> > ("clk: qcom: gcc-sdm845: Use floor ops for sdcc clks") but it seems
> > silly to do so when you could just go read that commit.
> >
> > NOTE: this is actually extra terrible because we're missing the 50 MHz
> > rate in the table (see the next patch AKA ("clk: qcom: gcc-sc7180: Add
> > 50 MHz clock rate for SDC2")).  That means then when you run an older
> > SD card it'll try to clock it at 100 MHz when it's only specced to run
> > at 50 MHz max.  As you can probably guess that doesn't work super
> > well.
> >
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > Fixes: 17269568f726 ("clk: qcom: Add Global Clock controller (GCC) driver for SC7180")
> > ---
> > Taniya: can you please update whatever process is used to generate
> > these clock files to use floor for SD card clocks.  I hope you can
> > also scour through these files looking for similar problems on other
> > SoCs and submit patches for them.
>
> Any chance the consumer of this clk can call clk_round_rate() and WARN()
> if the rate is not anywhere near what it wants it to be? I fear that
> this problem will just keep coming up otherwise.

Good idea.  Posted ("[PATCH] mmc: sdhci-msm: Warn about overclocking
SD/MMC") [1].

I just checked for the clock being higher, not lower and I did a
normal print rather than a WARN splat.

Interestingly this shows that we were also overclocking the eMMC
during probe (though we end up at a proper rate in the end).  I saw
these transitory errors during boot:

[    6.287870] mmc0: Card appears overclocked; req 52000000 Hz, actual
100000000 Hz
[    6.295811] mmc0: Card appears overclocked; req 52000000 Hz, actual
100000000 Hz
[    6.312573] mmc0: Card appears overclocked; req 104000000 Hz,
actual 192000000 Hz

[1] https://lore.kernel.org/r/20201210125709.1.Iec3430c7d3c2a29262695edef7b82a14aaa567e5@changeid

-Doug