Re: [PATCH v3] mmc: sdhci-msm: Warn about overclocking SD/MMC

[Adrian Hunter]

On 10/12/20 11:27 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].
> 
> [1] http://lore.kernel.org/r/20201210102234.1.I096779f219625148900fc984dd0084ed1ba87c7f@changeid
> 
> Suggested-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> ---
> 
> 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);

How does a warning help?

Also, did you consider setting host->mmc->actual_clock

> +
>  	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 */
>