Re: [PATCH 04/10] mci: add HS400 mode selection

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Sascha,

On 5/11/26 2:07 PM, Sascha Hauer wrote:
> eMMC HS400 transitions through HS and 8-bit DDR per JEDEC, on top of
> a card already tuned in HS200. Wire that up in the core:
> 
> - mmc_select_max_dtr() now records EXT_CSD_CARD_TYPE_HS400_{1_8V,1_2V}
>   in mmc_avail_type when both the host (mmc-hs400-1_8v / mmc-hs400-1_2v
>   in DT) and the card advertise it. HS400 reuses hs200_max_dtr (200 MHz)
>   since it's the same SDCLK rate, just DDR-sampled.
> 
> - mmc_set_bus_speed() treats HS200 and HS400 as the same rate tier.
> 
> - mmc_select_hs400() implements the JEDEC sequence:
>     1. CMD6 EXT_CSD_HS_TIMING = HS
>     2. host: MMC_TIMING_MMC_HS, clock = hs_max_dtr
>     3. CMD6 EXT_CSD_BUS_WIDTH = EXT_CSD_DDR_BUS_WIDTH_8
>     4. CMD6 EXT_CSD_HS_TIMING = HS400
>     5. host: MMC_TIMING_MMC_HS400, clock back to 200 MHz
> 
>   Bails early if the card lacks HS400 capability or the bus isn't 8-bit.
> 
> - mci_startup_mmc() runs mmc_select_hs400() right after a successful
>   HS200 tuning when EXT_CSD_CARD_TYPE_HS400 is in mmc_avail_type.
> 
> - mmc_card_hs400() helper added in mci.h, mirroring mmc_card_hs200().
> 
> Host drivers must additionally handle MMC_TIMING_MMC_HS400 in their
> set_ios / set_clock paths (e.g. setting the controller-specific HS400
> bit in HOST_CONTROL2, configuring data-strobe sampling). Without that
> the core will run the transition but the host won't sample correctly.

This patch is missing the downgrade code. If HS400 doesn't work out, we
should fallback to HS200.

Cheers,
Ahmad

> 
> Assisted-by: Claude Opus 4.7 <noreply@anthropic.com>
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> ---
>  drivers/mci/mci-core.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++--
>  include/mci.h          |  5 ++++
>  2 files changed, 82 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mci/mci-core.c b/drivers/mci/mci-core.c
> index 23b9117869..58b28ec653 100644
> --- a/drivers/mci/mci-core.c
> +++ b/drivers/mci/mci-core.c
> @@ -126,7 +126,8 @@ static int mci_set_blocklen(struct mci *mci, unsigned len)
>  {
>  	struct mci_cmd cmd = {0};
>  
> -	if (mci->host->ios.timing == MMC_TIMING_MMC_DDR52)
> +	if (mci->host->ios.timing == MMC_TIMING_MMC_DDR52 ||
> +	    mmc_card_hs400(mci))
>  		return 0;
>  
>  	mci_setup_cmd(&cmd, MMC_CMD_SET_BLOCKLEN, len, MMC_RSP_R1);
> @@ -1051,6 +1052,8 @@ static const char *mci_timing_tostr(unsigned timing)
>  		return "MMC DDR52";
>  	case MMC_TIMING_MMC_HS200:
>  		return "HS200";
> +	case MMC_TIMING_MMC_HS400:
> +		return "HS400";
>  	default:
>  		return "unknown"; /* shouldn't happen */
>  	}
> @@ -1783,6 +1786,18 @@ static void mmc_select_max_dtr(struct mci *mci)
>  		avail_type |= EXT_CSD_CARD_TYPE_HS200_1_2V;
>  	}
>  
> +	if ((caps2 & MMC_CAP2_HS400_1_8V) &&

This bit is not decoded in mci_print_caps (same or _1_2V)


> +	    (card_type & EXT_CSD_CARD_TYPE_HS400_1_8V)) {
> +		hs200_max_dtr = MMC_HS200_MAX_DTR;
> +		avail_type |= EXT_CSD_CARD_TYPE_HS400_1_8V;
> +	}
> +
> +	if ((caps2 & MMC_CAP2_HS400_1_2V) &&
> +	    (card_type & EXT_CSD_CARD_TYPE_HS400_1_2V)) {
> +		hs200_max_dtr = MMC_HS200_MAX_DTR;
> +		avail_type |= EXT_CSD_CARD_TYPE_HS400_1_2V;
> +	}
> +
>  	mci->host->hs200_max_dtr = hs200_max_dtr;
>  	mci->host->hs_max_dtr = hs_max_dtr;
>  	mci->host->mmc_avail_type = avail_type;
> @@ -1875,7 +1890,7 @@ static void mmc_set_bus_speed(struct mci *mci)
>  {
>  	unsigned int max_dtr = (unsigned int)-1;
>  
> -	if (mmc_card_hs200(mci) &&
> +	if ((mmc_card_hs200(mci) || mmc_card_hs400(mci)) &&
>  		max_dtr > mci->host->hs200_max_dtr)
>  		max_dtr = mci->host->hs200_max_dtr;
>  	else if (mmc_card_hs(mci) && max_dtr > mci->host->hs_max_dtr)
> @@ -1921,6 +1936,62 @@ int mmc_hs200_tuning(struct mci *mci)
>  	return mci_execute_tuning(mci);
>  }
>  
> +/*
> + * Switch from HS200 to HS400 per JEDEC. The card must already be in HS200
> + * (with successful tuning) and 8-bit bus width. The transition sequence is:
> + *
> + *   1. Switch the card back to HS timing.
> + *   2. Drop the host clock to HS rate (<= 52 MHz).
> + *   3. Switch the card to 8-bit DDR bus width.
> + *   4. Switch the card to HS400 timing.
> + *   5. Switch the host to HS400 timing and ramp the clock back to HS200 rate
> + *      (200 MHz, used as DDR so effective 400 MHz / 8-bit data lane).
> + */
> +static int mmc_select_hs400(struct mci *mci)
> +{
> +	struct mci_host *host = mci->host;
> +	int err;
> +	u8 val;
> +
> +	if (!(host->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400) ||
> +	    host->ios.bus_width != MMC_BUS_WIDTH_8)
> +		return 0;
> +
> +	/* Step 1: switch card back to HS timing */
> +	err = mci_switch(mci, EXT_CSD_HS_TIMING, EXT_CSD_TIMING_HS);
> +	if (err) {
> +		dev_err(&mci->dev, "switch to HS from HS200 failed: %d\n", err);
> +		return err;
> +	}
> +
> +	/* Step 2: drop host clock to HS rate */
> +	mci_set_timing(mci, MMC_TIMING_MMC_HS);
> +	mci_set_clock(mci, host->hs_max_dtr);

i.MX eSDHC implements ops.hs400_prepare_ddr here, but I guess it's ok to
skip until we add HS400 support there.

> +
> +	/* Step 3: switch card to 8-bit DDR */
> +	err = mci_switch(mci, EXT_CSD_BUS_WIDTH, EXT_CSD_DDR_BUS_WIDTH_8);
> +	if (err) {
> +		dev_err(&mci->dev, "switch to DDR for HS400 failed: %d\n", err);
> +		return err;
> +	}
> +> +	/* Step 4: switch card to HS400 timing */
> +	val = EXT_CSD_TIMING_HS400 | (host->drive_strength << EXT_CSD_DRV_STR_SHIFT);
> +	err = mci_switch(mci, EXT_CSD_HS_TIMING, val);
> +	if (err) {
> +		dev_err(&mci->dev, "switch to HS400 failed: %d\n", err);
> +		return err;
> +	}
> +
> +	/* Step 5: switch host to HS400 timing and ramp clock */
> +	mci_set_timing(mci, MMC_TIMING_MMC_HS400);
> +	mmc_set_bus_speed(mci);
> +
> +	dev_dbg(&mci->dev, "HS400 selected\n");
> +
> +	return 0;
> +}
> +
>  static int mci_startup_mmc(struct mci *mci)
>  {
>  	struct mci_host *host = mci->host;
> @@ -1947,6 +2018,10 @@ static int mci_startup_mmc(struct mci *mci)
>  			ret = mmc_hs200_tuning(mci);
>  			if (!ret) {
>  				dev_dbg(&mci->dev, "HS200 tuning succeeded\n");
> +
> +				if (host->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400)
> +					mmc_select_hs400(mci);
> +
>  				return 0;
>  			}
>  
> diff --git a/include/mci.h b/include/mci.h
> index 8348f97432..a7cd0c5ae2 100644
> --- a/include/mci.h
> +++ b/include/mci.h
> @@ -802,4 +802,9 @@ static inline bool mmc_card_hs200(struct mci *mci)
>  	return mci->host->ios.timing == MMC_TIMING_MMC_HS200;
>  }
>  
> +static inline bool mmc_card_hs400(struct mci *mci)
> +{
> +	return mci->host->ios.timing == MMC_TIMING_MMC_HS400;
> +}
> +
>  #endif /* _MCI_H_ */
> 

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