[U-Boot] [PATCH 37/41] mmc: fsl_esdhc: fix sd/mmc ddr mode clock setting issue

[Benoît Thébaudeau]

Dear Peng Fan,

On Mon, May 28, 2018 at 2:25 PM, Peng Fan <peng.fan at nxp.com> wrote:
> From: Ye Li <ye.li at nxp.com>
>
> When sd/mmc work at DDR mode, like HS400/HS400ES/DDR52/DDR50 mode,
> the actual clock rate is just half of the expected clock.
>
> This patch set the DDR_EN bit first for DDR mode, hardware divide
> the usdhc clock automatically, then follow the original sdr clock
> setting method.
>
> Signed-off-by: Haibo Chen <haibo.chen at nxp.com>
> Signed-off-by: Ye Li <ye.li at nxp.com>
> ---
>  drivers/mmc/fsl_esdhc.c | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/fsl_esdhc.c b/drivers/mmc/fsl_esdhc.c
> index 1b062ff06d..bf4ae74847 100644
> --- a/drivers/mmc/fsl_esdhc.c
> +++ b/drivers/mmc/fsl_esdhc.c
> @@ -583,18 +583,32 @@ static void set_sysctl(struct fsl_esdhc_priv *priv, struct mmc *mmc, uint clock)
>  #else
>         int pre_div = 2;
>  #endif
> -       int ddr_pre_div = mmc->ddr_mode ? 2 : 1;
>         int sdhc_clk = priv->sdhc_clk;
>         uint clk;
>
> +       /*
> +        * For ddr mode, usdhc need to enable DDR mode first, after select
> +        * this DDR mode, usdhc will automatically divide the usdhc clock
> +        */
> +       if (mmc->ddr_mode) {
> +               writel(readl(&regs->mixctrl) | MIX_CTRL_DDREN, &regs->mixctrl);
> +               sdhc_clk >>= 1;
> +       }
> +
>         if (clock < mmc->cfg->f_min)
>                 clock = mmc->cfg->f_min;
>
> -       while (sdhc_clk / (16 * pre_div * ddr_pre_div) > clock && pre_div < 256)
> -               pre_div *= 2;
> +       if ((sdhc_clk / 16) > clock) {
> +               for (; pre_div < 256; pre_div *= 2)
> +                       if ((sdhc_clk / pre_div) <= (clock * 16))
> +                               break;
> +       } else {
> +               pre_div = 1;

This value is not always available for this divider. See the
conditions in the initialization of this variable giving its minimum
value.

> +       }
>
> -       while (sdhc_clk / (div * pre_div * ddr_pre_div) > clock && div < 16)
> -               div++;
> +       for (div = 1; div <= 16; div++)
> +               if ((sdhc_clk / (div * pre_div)) <= clock)
> +                       break;
>
>         pre_div >>= 1;
>         div -= 1;

Best regards,
Benoît