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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Wed, 13 Feb 2019 13:08:43 +0100
Message-ID: <CAPDyKFpNEhXT0dD_p85Ab2H_nHtr5r86BLcvkLVUsdwtYLUs4g@mail.gmail.com>
Subject: Re: [PATCH v1] mmc: mmc: Fix HS setting in mmc_hs400_to_hs200()
To:     Chaotian Jing <chaotian.jing@mediatek.com>
Cc:     Matthias Brugger <matthias.bgg@gmail.com>,
        Shawn Lin <shawn.lin@rock-chips.com>,
        Simon Horman <horms+renesas@verge.net.au>,
        Kyle Roeschley <kyle.roeschley@ni.com>,
        Hongjie Fang <hongjiefang@asrmicro.com>,
        Harish Jenny K N <harish_kandiga@mentor.com>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-mediatek@lists.infradead.org,
        srv_heupstream <srv_heupstream@mediatek.com>,
        Adrian Hunter <adrian.hunter@intel.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Wed, 13 Feb 2019 at 10:07, Chaotian Jing <chaotian.jing@mediatek.com> wrote:
>
> mmc_hs400_to_hs200() begins with the card and host in HS400 mode.
> Therefore, any commands sent to the card should use HS400 timing.
> reduce clock frequency to 50Mhz but without host timming change
> may cause CMD6 response CRC error. because host still running at
> hs400 mode, and it's hard to find a suitable setting for all eMMC
> cards when clock frequency reduced to 50Mhz but card & host still
> in hs400 mode.
> this patch refers to mmc_select_hs400(), make the reduce clock frequency
> after card timing change.
>
> Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
> Fixes: ef3d232245ab ("mmc: mmc: Relax checking for switch errors after HS200 switch")
> ---
>  drivers/mmc/core/mmc.c | 29 +++++++++++++++++++++++------
>  1 file changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 09c688f..00adc2d 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1239,20 +1239,37 @@ int mmc_hs400_to_hs200(struct mmc_card *card)
>         int err;
>         u8 val;
>
> -       /* Reduce frequency to HS */
> -       max_dtr = card->ext_csd.hs_max_dtr;
> -       mmc_set_clock(host, max_dtr);
> -
>         /* Switch HS400 to HS DDR */
>         val = EXT_CSD_TIMING_HS;
>         err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING,
>                            val, card->ext_csd.generic_cmd6_time, 0,
>                            true, false, true);
> -       if (err)
> -               goto out_err;
> +       /*
> +        * as we are on the way to do re-tune, so if the CMD6 got response CRC
> +        * error, do not treat it as error.
> +        */
> +       if (err) {
> +               if (err == -EILSEQ) {
> +                       /*
> +                        * card will busy after sending out response and host
> +                        * driver may not wait busy de-assert when get
> +                        * response CRC error. so just wait enough time to
> +                        * ensure card leave busy state.
> +                        */
> +                       mmc_delay(card->ext_csd.generic_cmd6_time);
> +                       pr_debug("%s: %s switch to HS got CRC error\n",
> +                                mmc_hostname(host), __func__);
> +               } else {
> +                       goto out_err;
> +               }
> +       }
>
>         mmc_set_timing(host, MMC_TIMING_MMC_DDR52);
>
> +       /* Reduce frequency to HS */
> +       max_dtr = card->ext_csd.hs_max_dtr;
> +       mmc_set_clock(host, max_dtr);
> +

What Adrian suggested was to not to move this part, but instead, only
allow CRC errors from the CMD6 as above.

I guess it didn't work for you?

>         err = mmc_switch_status(card);
>         if (err)
>                 goto out_err;
> --
> 1.8.1.1.dirty
>

Kind regards
Uffe