phy: miphy28lp: Tune tx impedance across Soc cuts

This patch to compensate tx impedance (Sata, PCIe)
depending on Soc cuts the kernel is built for.

Signed-off-by: Giuseppe Condorelli <giuseppe.condorelli@st.com>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@linaro.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/phy-miphy28lp.txt

@@ -40,6 +40,7 @@ Optional properties (port (child) node):
 - st,px_rx_pol_inv	: to invert polarity of RXn/RXp (respectively negative line and positive
 			  line).
 - st,scc-on		: enable ssc to reduce effects of EMI (only for sata or PCIe).
+- st,tx-impedance-comp	: to compensate tx impedance avoiding out of range values.
 
 example:
 

drivers/phy/phy-miphy28lp.c

@@ -204,6 +204,7 @@ struct miphy28lp_phy {
 	bool osc_rdy;
 	bool px_rx_pol_inv;
 	bool ssc;
+	bool tx_impedance;
 
 	struct reset_control *miphy_rst;
 
@@ -632,6 +633,12 @@ static void miphy_pcie_tune_ssc(struct miphy28lp_phy *miphy_phy)
 	}
 }
 
+static inline void miphy_tune_tx_impedance(struct miphy28lp_phy *miphy_phy)
+{
+	/* Compensate Tx impedance to avoid out of range values */
+	writeb_relaxed(0x02, miphy_phy->base + MIPHY_COMP_POSTP);
+}
+
 static inline int miphy28lp_configure_sata(struct miphy28lp_phy *miphy_phy)
 {
 	void __iomem *base = miphy_phy->base;
@@ -670,6 +677,9 @@ static inline int miphy28lp_configure_sata(struct miphy28lp_phy *miphy_phy)
 	if (miphy_phy->ssc)
 		miphy_sata_tune_ssc(miphy_phy);
 
+	if (miphy_phy->tx_impedance)
+		miphy_tune_tx_impedance(miphy_phy);
+
 	return 0;
 }
 
@@ -703,6 +713,9 @@ static inline int miphy28lp_configure_pcie(struct miphy28lp_phy *miphy_phy)
 	if (miphy_phy->ssc)
 		miphy_pcie_tune_ssc(miphy_phy);
 
+	if (miphy_phy->tx_impedance)
+		miphy_tune_tx_impedance(miphy_phy);
+
 	return 0;
 }
 
@@ -1154,6 +1167,9 @@ static int miphy28lp_of_probe(struct device_node *np,
 
 	miphy_phy->ssc = of_property_read_bool(np, "st,ssc-on");
 
+	miphy_phy->tx_impedance =
+		of_property_read_bool(np, "st,tx-impedance-comp");
+
 	of_property_read_u32(np, "st,sata-gen", &miphy_phy->sata_gen);
 	if (!miphy_phy->sata_gen)
 		miphy_phy->sata_gen = SATA_GEN1;