phy: rockchip-emmc: Allow to set drive impedance via DTS.

The rockchip-emmc PHY can be configured with different
drive impedance values. Currenlty a value of 50 Ohm is
hard coded into the driver.

This patch introduces the DTS property 'drive-impedance-ohm'
for the rockchip-emmc phy node, which uses the value from the DTS
to setup the drive impedance accordingly.

Signed-off-by: Christoph Muellner <[e-mail]>
Signed-off-by: Philipp Tomsich <[e-mail]>
Reviewed-by: Heiko Stuebner <[e-mail]>
Signed-off-by: Kishon Vijay Abraham I <[e-mail]>

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

···
 	unsigned int	reg_offset;
 	struct regmap	*reg_base;
 	struct clk	*emmcclk;
+	unsigned int drive_impedance;
 };
 
 static int rockchip_emmc_phy_power(struct phy *phy, bool on_off)
···
 {
 	struct rockchip_emmc_phy *rk_phy = phy_get_drvdata(phy);
 
-	/* Drive impedance: 50 Ohm */
+	/* Drive impedance: from DTS */
 	regmap_write(rk_phy->reg_base,
 		     rk_phy->reg_offset + GRF_EMMCPHY_CON6,
-		     HIWORD_UPDATE(PHYCTRL_DR_50OHM,
+		     HIWORD_UPDATE(rk_phy->drive_impedance,
 				   PHYCTRL_DR_MASK,
 				   PHYCTRL_DR_SHIFT));
 
···
 	.owner		= THIS_MODULE,
 };
 
+static u32 convert_drive_impedance_ohm(struct platform_device *pdev, u32 dr_ohm)
+{
+	switch (dr_ohm) {
+	case 100:
+		return PHYCTRL_DR_100OHM;
+	case 66:
+		return PHYCTRL_DR_66OHM;
+	case 50:
+		return PHYCTRL_DR_50OHM;
+	case 40:
+		return PHYCTRL_DR_40OHM;
+	case 33:
+		return PHYCTRL_DR_33OHM;
+	}
+
+	dev_warn(&pdev->dev, "Invalid value %u for drive-impedance-ohm.\n",
+		 dr_ohm);
+	return PHYCTRL_DR_50OHM;
+}
+
 static int rockchip_emmc_phy_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
···
 	struct phy_provider *phy_provider;
 	struct regmap *grf;
 	unsigned int reg_offset;
+	u32 val;
 
 	if (!dev->parent || !dev->parent->of_node)
 		return -ENODEV;
···
 
 	rk_phy->reg_offset = reg_offset;
 	rk_phy->reg_base = grf;
+	rk_phy->drive_impedance = PHYCTRL_DR_50OHM;
+
+	if (!of_property_read_u32(dev->of_node, "drive-impedance-ohm", &val))
+		rk_phy->drive_impedance = convert_drive_impedance_ohm(pdev, val);
 
 	generic_phy = devm_phy_create(dev, dev->of_node, &ops);
 	if (IS_ERR(generic_phy)) {