Re: [PATCH 4/4] mmc: sdhci-cadence: read SD6HC DDR50 tuning from device tree

[Adrian Hunter]

On 22/09/2026 14:12, tze.yee.ng@xxxxxxxxxx wrote:
> From: Tze Yee Ng <tze.yee.ng@xxxxxxxxxx>
> 
> DDR50 has no CMD19 tuning, so the SD6HC read path relies on static PHY
> settings that need board/SoC characterisation. Read the read-DQS delay,
> read-DQS source and phony DQS assertion timing from the new
> cdns,ddr50-read-dqs-delay, cdns,ddr50-use-lpbk-dqs and
> cdns,ddr50-phony-dqs-timing DT properties at PHY probe, range-check them,

Firmware values are expected to be correct, and so are not validated.

> and apply them only in DDR50. When a property is absent the existing
> driver default is kept - for the phony DQS timing, the derived
> REBAR_PULSE_CYCLES-1.
> 
> Signed-off-by: Tze Yee Ng <tze.yee.ng@xxxxxxxxxx>
> ---
>  drivers/mmc/host/sdhci-cadence-phy-v6.c | 72 ++++++++++++++++++++++++-
>  1 file changed, 71 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/sdhci-cadence-phy-v6.c b/drivers/mmc/host/sdhci-cadence-phy-v6.c
> index 84592ae42762..0f47fa62d894 100644
> --- a/drivers/mmc/host/sdhci-cadence-phy-v6.c
> +++ b/drivers/mmc/host/sdhci-cadence-phy-v6.c
> @@ -129,6 +129,11 @@ struct sdhci_cdns6_phy {
>  	/* Active delay element (ps); doubled when one SDMCLK requires > 256 steps */
>  	u32 delay_element;
>  
> +	/* DDR read-path overrides (SoC-specific) */
> +	s32 ddr_read_dqs_delay;
> +	s32 ddr_use_lpbk_dqs;
> +	s32 ddr_phony_dqs_timing;
> +
>  	/* PHY_DLL_SLAVE_CTRL register fields */
>  	u8 cp_read_dqs_cmd_delay;	/* bits [31:24] */
>  	u8 cp_clk_wrdqs_delay;		/* bits [23:16] */
> @@ -145,6 +150,7 @@ struct sdhci_cdns6_phy {
>  	/* PHY_DQS_TIMING register fields */
>  	bool cp_use_phony_dqs;		/* bit [20] */
>  	bool cp_use_phony_dqs_cmd;	/* bit [19] */
> +	bool cp_use_lpbk_dqs;		/* bit [21] */
>  
>  	/* PHY_CTRL register fields */
>  	u32 cp_phony_dqs_timing;
> @@ -523,6 +529,12 @@ static void sdhci_cdns6_phy_calc_dat_in(struct sdhci_cdns6_phy *phy)
>  	if (phy->mode == MMC_TIMING_MMC_HS200)
>  		phy->cp_read_dqs_delay = phy->hs200_tune_val;
>  
> +	if (phy->mode == MMC_TIMING_UHS_DDR50 && phy->ddr_read_dqs_delay >= 0)
> +		phy->cp_read_dqs_delay = phy->ddr_read_dqs_delay &
> +			SDHCI_CDNS6_PHY_DLL_SLAVE_CTRL_READ_DQS_DELAY;

So here is unnecessarily assuming DT is providing a bad value.  It could just be:

	if (phy->mode == MMC_TIMING_UHS_DDR50 && phy->ddr_read_dqs_delay >= 0)
		phy->cp_read_dqs_delay = phy->ddr_read_dqs_delay;

> +
> +	phy->cp_use_lpbk_dqs = 1;
> +
>  	if (phy->sdhc_extended_rd_mode &&
>  	    (phy->mode == MMC_TIMING_UHS_DDR50 ||
>  	     phy->mode == MMC_TIMING_MMC_DDR52))
> @@ -530,6 +542,18 @@ static void sdhci_cdns6_phy_calc_dat_in(struct sdhci_cdns6_phy *phy)
>  	else
>  		phy->cp_phony_dqs_timing = 0;
>  
> +	if (phy->mode == MMC_TIMING_UHS_DDR50 && phy->ddr_use_lpbk_dqs >= 0)
> +		phy->cp_use_lpbk_dqs = phy->ddr_use_lpbk_dqs &
> +			FIELD_MAX(SDHCI_CDNS6_PHY_DQS_TIMING_USE_LPBK_DQS);

Ditto

> +
> +	/*
> +	 * The phony DQS timing derived above depends on the board's SD flight
> +	 * time, so allow a DT override to re-position the fabricated strobe.
> +	 */
> +	if (phy->mode == MMC_TIMING_UHS_DDR50 && phy->ddr_phony_dqs_timing >= 0)
> +		phy->cp_phony_dqs_timing = phy->ddr_phony_dqs_timing &
> +			FIELD_MAX(SDHCI_CDNS6_PHY_CTRL_PHONY_DQS_TIMING);

Ditto

> +
>  	if (strobe_dat) {
>  		/* dqs loopback input via IO cell */
>  		hcsdclkadj += phy->iocell_input_delay;
> @@ -693,10 +717,11 @@ int sdhci_cdns6_phy_init(struct sdhci_cdns_priv *priv)
>  	sdhci_cdns6_dll_reset(priv, true);
>  
>  	reg = sdhci_cdns6_read_phy_reg(priv, SDHCI_CDNS6_PHY_DQS_TIMING_REG);
> +	reg &= ~SDHCI_CDNS6_PHY_DQS_TIMING_USE_LPBK_DQS;
>  	reg &= ~SDHCI_CDNS6_PHY_DQS_TIMING_USE_PHONY_DQS;
>  	reg &= ~SDHCI_CDNS6_PHY_DQS_TIMING_USE_PHONY_DQS_CMD;
>  	reg |= SDHCI_CDNS6_PHY_DQS_TIMING_USE_EXT_LPBK_DQS;
> -	reg |= SDHCI_CDNS6_PHY_DQS_TIMING_USE_LPBK_DQS;
> +	reg |= FIELD_PREP(SDHCI_CDNS6_PHY_DQS_TIMING_USE_LPBK_DQS, phy->cp_use_lpbk_dqs);
>  	reg |= FIELD_PREP(SDHCI_CDNS6_PHY_DQS_TIMING_USE_PHONY_DQS, phy->cp_use_phony_dqs);
>  	reg |= FIELD_PREP(SDHCI_CDNS6_PHY_DQS_TIMING_USE_PHONY_DQS_CMD, phy->cp_use_phony_dqs_cmd);
>  	sdhci_cdns6_write_phy_reg(priv, SDHCI_CDNS6_PHY_DQS_TIMING_REG, reg);
> @@ -881,6 +906,7 @@ int sdhci_cdns6_phy_probe(struct platform_device *pdev, struct sdhci_cdns_priv *
>  	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>  	struct sdhci_cdns6_phy *phy;
>  	unsigned long val;
> +	u32 prop;
>  	int ret;
>  
>  	phy = devm_kzalloc(dev, sizeof(*phy), GFP_KERNEL);
> @@ -919,6 +945,50 @@ int sdhci_cdns6_phy_probe(struct platform_device *pdev, struct sdhci_cdns_priv *
>  
>  	phy->delay_element_org = phy->delay_element;
>  
> +	/*
> +	 * Optional DDR50 read-path tuning. These are board/card-characterised
> +	 * values with no CMD19 tuning in DDR50; absence keeps the driver
> +	 * default (-1 => not overridden).
> +	 */
> +	phy->ddr_read_dqs_delay = -1;
> +	if (!of_property_read_u32(dev->of_node, "cdns,ddr50-read-dqs-delay",
> +				  &prop)) {
> +		if (prop > SDHCI_CDNS6_PHY_DLL_SLAVE_CTRL_READ_DQS_DELAY) {
> +			dev_warn(dev,
> +				 "cdns,ddr50-read-dqs-delay %u out of range, clamping to %lu\n",
> +				 prop,
> +				 (unsigned long)SDHCI_CDNS6_PHY_DLL_SLAVE_CTRL_READ_DQS_DELAY);
> +			prop = SDHCI_CDNS6_PHY_DLL_SLAVE_CTRL_READ_DQS_DELAY;
> +		}
> +		phy->ddr_read_dqs_delay = prop;
> +	}

If the unnecessary validation is dropped:

	phy->ddr_read_dqs_delay = -1;
	of_property_read_u32(dev->of_node, "cdns,ddr50-read-dqs-delay", &phy->ddr_read_dqs_delay);

etc

> +
> +	phy->ddr_use_lpbk_dqs = -1;
> +	if (!of_property_read_u32(dev->of_node, "cdns,ddr50-use-lpbk-dqs",
> +				  &prop)) {
> +		if (prop > FIELD_MAX(SDHCI_CDNS6_PHY_DQS_TIMING_USE_LPBK_DQS)) {
> +			dev_warn(dev,
> +				 "cdns,ddr50-use-lpbk-dqs %u out of range, clamping to %lu\n",
> +				 prop,
> +				 (unsigned long)FIELD_MAX(SDHCI_CDNS6_PHY_DQS_TIMING_USE_LPBK_DQS));
> +			prop = FIELD_MAX(SDHCI_CDNS6_PHY_DQS_TIMING_USE_LPBK_DQS);
> +		}
> +		phy->ddr_use_lpbk_dqs = prop;
> +	}
> +
> +	phy->ddr_phony_dqs_timing = -1;
> +	if (!of_property_read_u32(dev->of_node, "cdns,ddr50-phony-dqs-timing",
> +				  &prop)) {
> +		if (prop > FIELD_MAX(SDHCI_CDNS6_PHY_CTRL_PHONY_DQS_TIMING)) {
> +			dev_warn(dev,
> +				 "cdns,ddr50-phony-dqs-timing %u out of range, clamping to %lu\n",
> +				 prop,
> +				 (unsigned long)FIELD_MAX(SDHCI_CDNS6_PHY_CTRL_PHONY_DQS_TIMING));
> +			prop = FIELD_MAX(SDHCI_CDNS6_PHY_CTRL_PHONY_DQS_TIMING);
> +		}
> +		phy->ddr_phony_dqs_timing = prop;
> +	}
> +
>  	priv->phy = phy;
>  
>  	return 0;