Re: [PATCH v5 1/2] mmc: sdhci-msm: Warn about overclocking SD/MMC

[Ulf Hansson <ulf.hansson@linaro.org>]

On Mon, 14 Dec 2020 at 18:23, Douglas Anderson <dianders@chromium.org> wrote:
>
> As talked about in commit 5e4b7e82d497 ("clk: qcom: gcc-sdm845: Use
> floor ops for sdcc clks"), most clocks handled by the Qualcomm clock
> drivers are rounded _up_ by default instead of down.  We should make
> sure SD/MMC clocks are always rounded down in the clock drivers.
> Let's add a warning in the Qualcomm SDHCI driver to help catch the
> problem.
>
> This would have saved a bunch of time [1].
>
> NOTE: this doesn't actually fix any problems, it just makes it obvious
> to devs that there is a problem and that should be an indication to
> fix the clock driver.
>
> [1] http://lore.kernel.org/r/20201210102234.1.I096779f219625148900fc984dd0084ed1ba87c7f@changeid
>
> Suggested-by: Stephen Boyd <swboyd@chromium.org>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Stephen Boyd <swboyd@chromium.org>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Applied for next, thanks!

Kind regards
Uffe


> ---
>
> (no changes since v4)
>
> Changes in v4:
> - Emphasize in the commit message that this itself doesn't fix anything.
>
> Changes in v3:
> - Proper printf format code.
>
> Changes in v2:
> - Store rate in unsigned long, not unsigned int.
> - Reuse the clk_get_rate() in the later print.
>
>  drivers/mmc/host/sdhci-msm.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
> index 3451eb325513..50beb407dbe9 100644
> --- a/drivers/mmc/host/sdhci-msm.c
> +++ b/drivers/mmc/host/sdhci-msm.c
> @@ -353,6 +353,7 @@ static void msm_set_clock_rate_for_bus_mode(struct sdhci_host *host,
>         struct sdhci_msm_host *msm_host = sdhci_pltfm_priv(pltfm_host);
>         struct mmc_ios curr_ios = host->mmc->ios;
>         struct clk *core_clk = msm_host->bulk_clks[0].clk;
> +       unsigned long achieved_rate;
>         int rc;
>
>         clock = msm_get_clock_rate_for_bus_mode(host, clock);
> @@ -363,10 +364,20 @@ static void msm_set_clock_rate_for_bus_mode(struct sdhci_host *host,
>                        curr_ios.timing);
>                 return;
>         }
> +
> +       /*
> +        * Qualcomm clock drivers by default round clock _up_ if they can't
> +        * make the requested rate.  This is not good for SD.  Yell if we
> +        * encounter it.
> +        */
> +       achieved_rate = clk_get_rate(core_clk);
> +       if (achieved_rate > clock)
> +               pr_warn("%s: Card appears overclocked; req %u Hz, actual %lu Hz\n",
> +                       mmc_hostname(host->mmc), clock, achieved_rate);
> +
>         msm_host->clk_rate = clock;
>         pr_debug("%s: Setting clock at rate %lu at timing %d\n",
> -                mmc_hostname(host->mmc), clk_get_rate(core_clk),
> -                curr_ios.timing);
> +                mmc_hostname(host->mmc), achieved_rate, curr_ios.timing);
>  }
>
>  /* Platform specific tuning */
> --
> 2.29.2.576.ga3fc446d84-goog
>