linux-kernel - Re: [PATCH v2] mmc: sdhci: fix minimum clock rate for v3 controller

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Message-ID: <7def4624-e1c5-6208-efaa-4f11f98fda6d@intel.com>
Date:   Wed, 15 Jan 2020 10:55:43 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mmc: sdhci: fix minimum clock rate for v3 controller

On 15/01/20 10:32 am, Michał Mirosław wrote:
> For SDHCIv3+ with programmable clock mode, minimal clock frequency is
> still base clock / max(divider). Minimal programmable clock frequency is
> always greater than minimal divided clock frequency. Without this patch,
> SDHCI uses out-of-spec initial frequency when multiplier is big enough:
> 
> mmc1: mmc_rescan_try_freq: trying to init card at 468750 Hz
> [for 480 MHz source clock divided by 1024]
> 
> The code in sdhci_calc_clk() already chooses a correct SDCLK clock source.

source -> mode

> 
> Cc: stable@...r.kernel.org
> Fixes: c3ed3877625f ("mmc: sdhci: add support for programmable clock mode")
> Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> ---
>  v2: extend commitmsg and add comment
> ---
>  drivers/mmc/host/sdhci.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 96609c961465..fde510c55c89 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -3903,11 +3903,11 @@ int sdhci_setup_host(struct sdhci_host *host)
>  	if (host->ops->get_min_clock)
>  		mmc->f_min = host->ops->get_min_clock(host);
>  	else if (host->version >= SDHCI_SPEC_300) {
> -		if (host->clk_mul) {
> -			mmc->f_min = (host->max_clk * host->clk_mul) / 1024;
> +		if (host->clk_mul)
>  			max_clk = host->max_clk * host->clk_mul;
> -		} else
> -			mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
> +		/* minimal divided clock rate is always less than minimal
> +		 * programmable clock rate */

Comment format and let's use the same terminology as the spec.

		/*
		 * Divided Clock Mode minimum clock rate is always less than
		 * Programmable Clock Mode minimum clock rate.
		 */

> +		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_300;
>  	} else
>  		mmc->f_min = host->max_clk / SDHCI_MAX_DIV_SPEC_200;
>  
>