phy: rockchip: set pulldown for strobe line in dts

This patch add support to set the internal pulldown via dt property
and allow simplify the board design for the trace from emmc-phy to
the eMMC chipset.
Default to not set the pull-down.

This patch was inspired from the 4.4 tree of the
Rockchip SDK, where it is enabled unconditional.
The patch had been tested with our rk3399 customized board.

Signed-off-by: Chris Ruehl <chris.ruehl@gtsys.com.hk>
Link: https://lore.kernel.org/r/20201129054416.3980-2-chris.ruehl@gtsys.com.hk
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/rockchip/phy-rockchip-emmc.c

@@ -67,6 +67,10 @@
 #define PHYCTRL_OTAPDLYENA_SHIFT	0xb
 #define PHYCTRL_OTAPDLYSEL_MASK		0xf
 #define PHYCTRL_OTAPDLYSEL_SHIFT	0x7
+#define PHYCTRL_REN_STRB_DISABLE	0x0
+#define PHYCTRL_REN_STRB_ENABLE		0x1
+#define PHYCTRL_REN_STRB_MASK		0x1
+#define PHYCTRL_REN_STRB_SHIFT		0x9
 
 #define PHYCTRL_IS_CALDONE(x) \
 	((((x) >> PHYCTRL_CALDONE_SHIFT) & \
@@ -80,6 +84,7 @@ struct rockchip_emmc_phy {
 	struct regmap	*reg_base;
 	struct clk	*emmcclk;
 	unsigned int drive_impedance;
+	unsigned int enable_strobe_pulldown;
 };
 
 static int rockchip_emmc_phy_power(struct phy *phy, bool on_off)
@@ -295,6 +300,13 @@ static int rockchip_emmc_phy_power_on(struct phy *phy)
 				   PHYCTRL_OTAPDLYSEL_MASK,
 				   PHYCTRL_OTAPDLYSEL_SHIFT));
 
+	/* Internal pull-down for strobe line */
+	regmap_write(rk_phy->reg_base,
+		     rk_phy->reg_offset + GRF_EMMCPHY_CON2,
+		     HIWORD_UPDATE(rk_phy->enable_strobe_pulldown,
+				   PHYCTRL_REN_STRB_MASK,
+				   PHYCTRL_REN_STRB_SHIFT));
+
 	/* Power up emmc phy analog blocks */
 	return rockchip_emmc_phy_power(phy, PHYCTRL_PDB_PWR_ON);
 }
@@ -359,10 +371,14 @@ static int rockchip_emmc_phy_probe(struct platform_device *pdev)
 	rk_phy->reg_offset = reg_offset;
 	rk_phy->reg_base = grf;
 	rk_phy->drive_impedance = PHYCTRL_DR_50OHM;
+	rk_phy->enable_strobe_pulldown = PHYCTRL_REN_STRB_DISABLE;
 
 	if (!of_property_read_u32(dev->of_node, "drive-impedance-ohm", &val))
 		rk_phy->drive_impedance = convert_drive_impedance_ohm(pdev, val);
 
+	if (of_property_read_bool(dev->of_node, "enable-strobe-pulldown"))
+		rk_phy->enable_strobe_pulldown = PHYCTRL_REN_STRB_ENABLE;
+
 	generic_phy = devm_phy_create(dev, dev->of_node, &ops);
 	if (IS_ERR(generic_phy)) {
 		dev_err(dev, "failed to create PHY\n");