linux-kernel - Re: [PATCH v4 2/2] mmc: sdhci-msm: Actually set the actual clock

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Date:   Mon, 14 Dec 2020 10:42:49 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Taniya Das <tdas@...eaurora.org>, vbadigan@...eaurora.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 v4 2/2] mmc: sdhci-msm: Actually set the actual clock

On Fri 11 Dec 11:12 CST 2020, Douglas Anderson wrote:

> The MSM SDHCI driver always set the "actual_clock" field to 0.  It had
> a comment about it not being needed because we weren't using the
> standard SDHCI divider mechanism and we'd just fallback to
> "host->clock".  However, it's still better to provide the actual
> clock.  Why?
> 
> 1. It will make timeout calculations slightly better.  On one system I
>    have, the eMMC requets 200 MHz (for HS400-ES) but actually gets 192
>    MHz.  These are close, but why not get the more accurate one.
> 
> 2. If things are seriously off in the clock driver and it's missing
>    rates or picking the wrong rate (maybe it's rounding up instead of
>    down), this will make it much more obvious what's going on.
> 
> NOTE: we have to be a little careful here because the "actual_clock"
> field shouldn't include the multiplier that sdhci-msm needs
> internally.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn

> ---
> 
> Changes in v4:
> - ("mmc: sdhci-msm: Actually set the actual clock") new for v4.
> 
>  drivers/mmc/host/sdhci-msm.c | 32 ++++++++++++++------------------
>  1 file changed, 14 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
> index 50beb407dbe9..08a3960001ad 100644
> --- a/drivers/mmc/host/sdhci-msm.c
> +++ b/drivers/mmc/host/sdhci-msm.c
> @@ -328,7 +328,7 @@ static void sdhci_msm_v5_variant_writel_relaxed(u32 val,
>  	writel_relaxed(val, host->ioaddr + offset);
>  }
>  
> -static unsigned int msm_get_clock_rate_for_bus_mode(struct sdhci_host *host,
> +static unsigned int msm_get_clock_mult_for_bus_mode(struct sdhci_host *host,
>  						    unsigned int clock)
>  {
>  	struct mmc_ios ios = host->mmc->ios;
> @@ -342,8 +342,8 @@ static unsigned int msm_get_clock_rate_for_bus_mode(struct sdhci_host *host,
>  	    ios.timing == MMC_TIMING_MMC_DDR52 ||
>  	    ios.timing == MMC_TIMING_MMC_HS400 ||
>  	    host->flags & SDHCI_HS400_TUNING)
> -		clock *= 2;
> -	return clock;
> +		return 2;
> +	return 1;
>  }
>  
>  static void msm_set_clock_rate_for_bus_mode(struct sdhci_host *host,
> @@ -354,14 +354,16 @@ static void msm_set_clock_rate_for_bus_mode(struct sdhci_host *host,
>  	struct mmc_ios curr_ios = host->mmc->ios;
>  	struct clk *core_clk = msm_host->bulk_clks[0].clk;
>  	unsigned long achieved_rate;
> +	unsigned int desired_rate;
> +	unsigned int mult;
>  	int rc;
>  
> -	clock = msm_get_clock_rate_for_bus_mode(host, clock);
> -	rc = dev_pm_opp_set_rate(mmc_dev(host->mmc), clock);
> +	mult = msm_get_clock_mult_for_bus_mode(host, clock);
> +	desired_rate = clock * mult;
> +	rc = dev_pm_opp_set_rate(mmc_dev(host->mmc), desired_rate);
>  	if (rc) {
>  		pr_err("%s: Failed to set clock at rate %u at timing %d\n",
> -		       mmc_hostname(host->mmc), clock,
> -		       curr_ios.timing);
> +		       mmc_hostname(host->mmc), desired_rate, curr_ios.timing);
>  		return;
>  	}
>  
> @@ -371,11 +373,12 @@ static void msm_set_clock_rate_for_bus_mode(struct sdhci_host *host,
>  	 * encounter it.
>  	 */
>  	achieved_rate = clk_get_rate(core_clk);
> -	if (achieved_rate > clock)
> +	if (achieved_rate > desired_rate)
>  		pr_warn("%s: Card appears overclocked; req %u Hz, actual %lu Hz\n",
> -			mmc_hostname(host->mmc), clock, achieved_rate);
> +			mmc_hostname(host->mmc), desired_rate, achieved_rate);
> +	host->mmc->actual_clock = achieved_rate / mult;
>  
> -	msm_host->clk_rate = clock;
> +	msm_host->clk_rate = desired_rate;
>  	pr_debug("%s: Setting clock at rate %lu at timing %d\n",
>  		 mmc_hostname(host->mmc), achieved_rate, curr_ios.timing);
>  }
> @@ -1756,13 +1759,6 @@ static unsigned int sdhci_msm_get_min_clock(struct sdhci_host *host)
>  static void __sdhci_msm_set_clock(struct sdhci_host *host, unsigned int clock)
>  {
>  	u16 clk;
> -	/*
> -	 * Keep actual_clock as zero -
> -	 * - since there is no divider used so no need of having actual_clock.
> -	 * - MSM controller uses SDCLK for data timeout calculation. If
> -	 *   actual_clock is zero, host->clock is taken for calculation.
> -	 */
> -	host->mmc->actual_clock = 0;
>  
>  	sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
>  
> @@ -1785,7 +1781,7 @@ static void sdhci_msm_set_clock(struct sdhci_host *host, unsigned int clock)
>  	struct sdhci_msm_host *msm_host = sdhci_pltfm_priv(pltfm_host);
>  
>  	if (!clock) {
> -		msm_host->clk_rate = clock;
> +		host->mmc->actual_clock = msm_host->clk_rate = 0;
>  		goto out;
>  	}
>  
> -- 
> 2.29.2.576.ga3fc446d84-goog
>