linux-kernel - Re: [PATCH v2] mmc: core: Set HS clock speed before sending HS CMD13

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Date:   Thu, 24 Mar 2022 13:12:48 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH v2] mmc: core: Set HS clock speed before sending HS CMD13

On Sat, 19 Mar 2022 at 02:52, Brian Norris <briannorris@...omium.org> wrote:
>
> Way back in commit 4f25580fb84d ("mmc: core: changes frequency to
> hs_max_dtr when selecting hs400es"), Rockchip engineers noticed that
> some eMMC don't respond to SEND_STATUS commands very reliably if they're
> still running at a low initial frequency. As mentioned in that commit,
> JESD84-B51 P49 suggests a sequence in which the host:
> 1. sets HS_TIMING
> 2. bumps the clock ("<= 52 MHz")
> 3. sends further commands
>
> It doesn't exactly require that we don't use a lower-than-52MHz
> frequency, but in practice, these eMMC don't like it.
>
> The aforementioned commit tried to get that right for HS400ES, although
> it's unclear whether this ever truly worked as committed into mainline,
> as other changes/refactoring adjusted the sequence in conflicting ways:
>
> 08573eaf1a70 ("mmc: mmc: do not use CMD13 to get status after speed mode
> switch")
>
> 53e60650f74e ("mmc: core: Allow CMD13 polling when switching to HS mode
> for mmc")
>
> In any case, today we do step 3 before step 2. Let's fix that, and also
> apply the same logic to HS200/400, where this eMMC has problems too.
>
> Resolves errors like this seen when booting some RK3399 Gru/Scarlet
> systems:
>
> [    2.058881] mmc1: CQHCI version 5.10
> [    2.097545] mmc1: SDHCI controller on fe330000.mmc [fe330000.mmc] using ADMA
> [    2.209804] mmc1: mmc_select_hs400es failed, error -84
> [    2.215597] mmc1: error -84 whilst initialising MMC card
> [    2.417514] mmc1: mmc_select_hs400es failed, error -110
> [    2.423373] mmc1: error -110 whilst initialising MMC card
> [    2.605052] mmc1: mmc_select_hs400es failed, error -110
> [    2.617944] mmc1: error -110 whilst initialising MMC card
> [    2.835884] mmc1: mmc_select_hs400es failed, error -110
> [    2.841751] mmc1: error -110 whilst initialising MMC card
>
> Fixes: 08573eaf1a70 ("mmc: mmc: do not use CMD13 to get status after speed mode switch")
> Fixes: 53e60650f74e ("mmc: core: Allow CMD13 polling when switching to HS mode for mmc")
> Fixes: 4f25580fb84d ("mmc: core: changes frequency to hs_max_dtr when selecting hs400es")
> Cc: Shawn Lin <shawn.lin@...k-chips.com>
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
>
> Changes in v2:
>  * Use ext_csd.hs200_max_dtr for HS200
>  * Retest on top of 3b6c472822f8 ("mmc: core: Improve fallback to speed
>    modes if eMMC HS200 fails")
>
>  drivers/mmc/core/mmc.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index e7ea45386c22..b75fa4b67964 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1385,12 +1385,17 @@ static int mmc_select_hs400es(struct mmc_card *card)
>         }
>
>         mmc_set_timing(host, MMC_TIMING_MMC_HS);
> +
> +       /*
> +        * Bump to HS frequency. Some cards don't handle SEND_STATUS reliably
> +        * at the initial frequency.
> +        */
> +       mmc_set_clock(host, card->ext_csd.hs_max_dtr);
> +
>         err = mmc_switch_status(card, true);
>         if (err)
>                 goto out_err;
>
> -       mmc_set_clock(host, card->ext_csd.hs_max_dtr);
> -
>         /* Switch card to DDR with strobe bit */
>         val = EXT_CSD_DDR_BUS_WIDTH_8 | EXT_CSD_BUS_WIDTH_STROBE;
>         err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
> @@ -1482,6 +1487,12 @@ static int mmc_select_hs200(struct mmc_card *card)
>                 old_timing = host->ios.timing;
>                 mmc_set_timing(host, MMC_TIMING_MMC_HS200);
>
> +               /*
> +                * Bump to HS200 frequency. Some cards don't handle SEND_STATUS
> +                * reliably at the initial frequency.
> +                */
> +               mmc_set_clock(host, card->ext_csd.hs200_max_dtr);
> +

If the mmc_switch_status() fails with -EBADMSG, we should probably
restore the clock to its previous value. Otherwise I think we could
potentially break the fallback implemented in 3b6c472822f8 ("mmc:
core: Improve fallback to speed modes if eMMC HS200 fails")

Moreover, this change means that we will be calling
mmc_set_bus_speed() from mmc_select_timing(), to actually set the same
HS200 clock rate again. That is unnecessary, can we please avoid that
in some way.

>                 /*
>                  * For HS200, CRC errors are not a reliable way to know the
>                  * switch failed. If there really is a problem, we would expect

Kind regards
Uffe