[PATCH v2 4/4] mmc: sdhci-cadence6: read SD6HC DDR50 tuning from device tree

[tze . yee . ng]

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,ddr-read-dqs-delay-ps, cdns,ddr-no-lpbk-dqs and
cdns,ddr-phony-dqs-timing DT properties at PHY probe and apply them in
the extended-read DDR modes (DDR50 and DDR52). The read-DQS delay is
given in picoseconds and converted to delay elements with
cdns,delay-element-ps; since that quotient depends on the element size,
it is clamped to the 8-bit PHY field maximum (255) to avoid wrap-around.

Loopback DQS is the recommended read-capture path and stays the default;
cdns,ddr-no-lpbk-dqs lets a board fall back to the fabricated phony DQS.
When a property is absent the driver-computed value is kept - for the
phony DQS timing, the value derived from the RE# pulse width
(REBAR_PULSE_CYCLES-1).

Signed-off-by: Tze Yee Ng <tze.yee.ng@xxxxxxxxxx>
---
Changes in v2:
- Updated patch title to "mmc: sdhci-cadence6:" since it touches only the
  v6 PHY.
- Renamed the properties to cdns,ddr-*.
- Read cdns,ddr-read-dqs-delay-ps in ps and convert it to delay elements 
  (dividing by cdns,delay-element-ps), clamping that quotient to the 8-bit
  PHY field. (Krzysztof Kozlowski)
- Read cdns,ddr-no-lpbk-dqs via of_property_read_bool(). (Krzysztof Kozlowski)
- Dropped the v1 per-property range checks and redundant FIELD_MAX() write
  masks. (Adrian Hunter)
- Apply the overrides in both DDR50 and DDR52.
---
 drivers/mmc/host/sdhci-cadence-phy-v6.c | 59 ++++++++++++++++++++++++-
 1 file changed, 58 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/host/sdhci-cadence-phy-v6.c b/drivers/mmc/host/sdhci-cadence-phy-v6.c
index 8d6a9c26c139..2b1b7256731a 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) */
+	u32 ddr_read_dqs_delay_ps;
+	bool ddr_no_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 +529,16 @@ 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->mode == MMC_TIMING_MMC_DDR52) && phy->ddr_read_dqs_delay_ps) {
+		u32 steps = phy->ddr_read_dqs_delay_ps / phy->delay_element_org;
+		u32 max_steps = FIELD_MAX(SDHCI_CDNS6_PHY_DLL_SLAVE_CTRL_READ_DQS_DELAY);
+
+		phy->cp_read_dqs_delay = min_t(u32, steps, max_steps);
+	}
+
+	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 +546,23 @@ static void sdhci_cdns6_phy_calc_dat_in(struct sdhci_cdns6_phy *phy)
 	else
 		phy->cp_phony_dqs_timing = 0;
 
+	/*
+	 * Loopback DQS is the recommended read-capture path; allow boards that
+	 * need the fabricated phony DQS instead to opt out in the DDR modes.
+	 */
+	if ((phy->mode == MMC_TIMING_UHS_DDR50 ||
+	     phy->mode == MMC_TIMING_MMC_DDR52) && phy->ddr_no_lpbk_dqs)
+		phy->cp_use_lpbk_dqs = 0;
+
+	/*
+	 * The computed phony DQS timing above is derived from the RE# pulse
+	 * width. Allow a DT override for boards whose flight time shifts the
+	 * returning DDR data relative to the fabricated strobe.
+	 */
+	if ((phy->mode == MMC_TIMING_UHS_DDR50 ||
+	     phy->mode == MMC_TIMING_MMC_DDR52) && phy->ddr_phony_dqs_timing >= 0)
+		phy->cp_phony_dqs_timing = phy->ddr_phony_dqs_timing;
+
 	if (strobe_dat) {
 		/* dqs loopback input via IO cell */
 		hcsdclkadj += phy->iocell_input_delay;
@@ -693,10 +726,11 @@ 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);
@@ -878,6 +912,7 @@ 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);
@@ -916,6 +951,28 @@ int sdhci_cdns6_phy_probe(struct platform_device *pdev, struct sdhci_cdns_priv *
 
 	phy->delay_element_org = phy->delay_element;
 
+	/*
+	 * Optional read-path tuning for the extended-read DDR modes (SD DDR50,
+	 * eMMC DDR52).
+	 */
+	phy->ddr_read_dqs_delay_ps = 0;
+	of_property_read_u32(dev->of_node, "cdns,ddr-read-dqs-delay-ps",
+			     &phy->ddr_read_dqs_delay_ps);
+	if (phy->ddr_read_dqs_delay_ps / phy->delay_element_org >
+	    FIELD_MAX(SDHCI_CDNS6_PHY_DLL_SLAVE_CTRL_READ_DQS_DELAY))
+		dev_warn(dev,
+			 "cdns,ddr-read-dqs-delay-ps %u too large, clamping to %lu elements\n",
+			 phy->ddr_read_dqs_delay_ps,
+			 (unsigned long)FIELD_MAX(SDHCI_CDNS6_PHY_DLL_SLAVE_CTRL_READ_DQS_DELAY));
+
+	phy->ddr_no_lpbk_dqs = of_property_read_bool(dev->of_node,
+						     "cdns,ddr-no-lpbk-dqs");
+
+	phy->ddr_phony_dqs_timing = -1;
+	if (!of_property_read_u32(dev->of_node, "cdns,ddr-phony-dqs-timing",
+				  &prop))
+		phy->ddr_phony_dqs_timing = prop;
+
 	priv->phy = phy;
 
 	return 0;
-- 
2.43.7