phy: rockchip-emmc: output tap delay dt property

Update the rockchip-emmc phy to set the otapdlysec register with
a dt property. This was mentioned from Brian Norris when he sent
the path to set the default value in the driver.
This patch add a dt property 'output-tapdelay-select' u32 and allow
to set the 0x0-0xf. If not set in dts, the old default 0x4 applies.

Tested with our customized rk3399 to tune the eMMC.

Signed-off-by: Chris Ruehl <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

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

···
 #define PHYCTRL_OTAPDLYENA		0x1
 #define PHYCTRL_OTAPDLYENA_MASK		0x1
 #define PHYCTRL_OTAPDLYENA_SHIFT	0xb
+#define PHYCTRL_OTAPDLYSEL_DEFAULT	0x4
+#define PHYCTRL_OTAPDLYSEL_MAXVALUE	0xf
 #define PHYCTRL_OTAPDLYSEL_MASK		0xf
 #define PHYCTRL_OTAPDLYSEL_SHIFT	0x7
 #define PHYCTRL_REN_STRB_DISABLE	0x0
···
 	struct clk	*emmcclk;
 	unsigned int drive_impedance;
 	unsigned int enable_strobe_pulldown;
+	unsigned int output_tapdelay_select;
 };
 
 static int rockchip_emmc_phy_power(struct phy *phy, bool on_off)
···
 	/* Output tap delay */
 	regmap_write(rk_phy->reg_base,
 		     rk_phy->reg_offset + GRF_EMMCPHY_CON0,
-		     HIWORD_UPDATE(4,
+		     HIWORD_UPDATE(rk_phy->output_tapdelay_select,
 				   PHYCTRL_OTAPDLYSEL_MASK,
 				   PHYCTRL_OTAPDLYSEL_SHIFT));
 
···
 	rk_phy->reg_base = grf;
 	rk_phy->drive_impedance = PHYCTRL_DR_50OHM;
 	rk_phy->enable_strobe_pulldown = PHYCTRL_REN_STRB_DISABLE;
+	rk_phy->output_tapdelay_select = PHYCTRL_OTAPDLYSEL_DEFAULT;
 
 	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;
+
+	if (!of_property_read_u32(dev->of_node, "output-tapdelay-select", &val)) {
+		if (val <= PHYCTRL_OTAPDLYSEL_MAXVALUE)
+			rk_phy->output_tapdelay_select = val;
+		else
+			dev_err(dev, "output-tapdelay-select exceeds limit, apply default\n");
+	}
 
 	generic_phy = devm_phy_create(dev, dev->of_node, &ops);
 	if (IS_ERR(generic_phy)) {