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

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Message-ID: <c4f59241-1b4b-363f-c786-71636514f233@intel.com>
Date:   Tue, 15 Dec 2020 10:24:08 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Douglas Anderson <dianders@...omium.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Taniya Das <tdas@...eaurora.org>, vbadigan@...eaurora.org,
        Stephen Boyd <swboyd@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org
Subject: Re: [PATCH v5 1/2] mmc: sdhci-msm: Warn about overclocking SD/MMC

On 14/12/20 7:21 pm, Douglas Anderson 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@...omium.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Acked-by: Adrian Hunter <adrian.hunter@...el.com>

> ---
> 
> (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 */
>