linux-kernel - Re: [PATCH 3/4] mmc: sdhci-esdhc-imx: Allow all supported prescaler values

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Date:   Mon, 29 May 2017 11:03:03 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Benoît Thébaudeau <benoit@...stem.com>,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Fabio Estevam <fabio.estevam@....com>,
        joancarles <joancarles@...ngenieria.es>,
        Eric Bénard <eric@...rea.com>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH 3/4] mmc: sdhci-esdhc-imx: Allow all supported prescaler
 values

On 03/05/17 13:05, Benoît Thébaudeau wrote:
> On i.MX, SYSCTL.SDCLKFS may always be set to 0 in order to make the SD
> clock frequency prescaler divide by 1 in SDR mode, even with the eSDHC.
> The previous minimum prescaler value of 2 in SDR mode with the eSDHC was
> a code remnant from PowerPC, which actually has this limitation on
> earlier revisions.
> 
> In DDR mode, the prescaler can divide by up to 512.
> 
> The maximum SD clock frequency in High Speed mode is 50 MHz. On i.MX25,
> this change makes it possible to get 48 MHz from the USB PLL
> (240 MHz / 5 / 1) instead of only 40 MHz from the USB PLL
> (240 MHz / 3 / 2) or 33.25 MHz from the AHB clock (133 MHz / 2 / 2).
> 
> Signed-off-by: Benoît Thébaudeau <benoit@...stem.com>

I would expect to see Acks from other sdhci-esdhc-imx users.  Nevertheless,
for sdhci:

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

> ---
>  drivers/mmc/host/sdhci-esdhc-imx.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
> index 4ee82e1..fa60d13 100644
> --- a/drivers/mmc/host/sdhci-esdhc-imx.c
> +++ b/drivers/mmc/host/sdhci-esdhc-imx.c
> @@ -674,7 +674,8 @@ static inline void esdhc_pltfm_set_clock(struct sdhci_host *host,
>  	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>  	struct pltfm_imx_data *imx_data = sdhci_pltfm_priv(pltfm_host);
>  	unsigned int host_clock = pltfm_host->clock;
> -	int pre_div = 2;
> +	int ddr_pre_div = imx_data->is_ddr ? 2 : 1;
> +	int pre_div = 1;
>  	int div = 1;
>  	u32 temp, val;
>  
> @@ -689,28 +690,23 @@ static inline void esdhc_pltfm_set_clock(struct sdhci_host *host,
>  		return;
>  	}
>  
> -	if (esdhc_is_usdhc(imx_data) && !imx_data->is_ddr)
> -		pre_div = 1;
> -
>  	temp = sdhci_readl(host, ESDHC_SYSTEM_CONTROL);
>  	temp &= ~(ESDHC_CLOCK_IPGEN | ESDHC_CLOCK_HCKEN | ESDHC_CLOCK_PEREN
>  		| ESDHC_CLOCK_MASK);
>  	sdhci_writel(host, temp, ESDHC_SYSTEM_CONTROL);
>  
> -	while (host_clock / pre_div / 16 > clock && pre_div < 256)
> +	while (host_clock / (16 * pre_div * ddr_pre_div) > clock &&
> +			pre_div < 256)
>  		pre_div *= 2;
>  
> -	while (host_clock / pre_div / div > clock && div < 16)
> +	while (host_clock / (div * pre_div * ddr_pre_div) > clock && div < 16)
>  		div++;
>  
> -	host->mmc->actual_clock = host_clock / pre_div / div;
> +	host->mmc->actual_clock = host_clock / (div * pre_div * ddr_pre_div);
>  	dev_dbg(mmc_dev(host->mmc), "desired SD clock: %d, actual: %d\n",
>  		clock, host->mmc->actual_clock);
>  
> -	if (imx_data->is_ddr)
> -		pre_div >>= 2;
> -	else
> -		pre_div >>= 1;
> +	pre_div >>= 1;
>  	div--;
>  
>  	temp = sdhci_readl(host, ESDHC_SYSTEM_CONTROL);
>