net: mdio: meson-gxl set 28th bit in eth_reg2

This bit is necessary to enable packets on the interface. Without this
bit set, ethernet behaves as if it is working but no activity occurs.

The vendor SDK sets this bit along with the PHY_ID bits. u-boot will set
this bit as well but if u-boot is not compiled with networking, the
interface will not work since it is missing this register bit set.

Cc: stable@vger.kernel.org
Fixes: 9a24e1f ("net: mdio: add amlogic gxl mdio mux support");
Signed-off-by: Da Xue <da@libre.computer>

Author: Da Xue

drivers/net/mdio/mdio-mux-meson-gxl.c

@@ -17,6 +17,7 @@
 #define  REG2_LEDACT		GENMASK(23, 22)
 #define  REG2_LEDLINK		GENMASK(25, 24)
 #define  REG2_DIV4SEL		BIT(27)
+#define  REG2_RESERVED_28	BIT(28)
 #define  REG2_ADCBYPASS		BIT(30)
 #define  REG2_CLKINSEL		BIT(31)
 #define ETH_REG3		0x4
@@ -65,7 +66,7 @@ static void gxl_enable_internal_mdio(struct gxl_mdio_mux *priv)
 	 * The only constraint is that it must match the one in
 	 * drivers/net/phy/meson-gxl.c to properly match the PHY.
 	 */
-	writel(FIELD_PREP(REG2_PHYID, EPHY_GXL_ID),
+	writel(REG2_RESERVED_28 | FIELD_PREP(REG2_PHYID, EPHY_GXL_ID),
 	       priv->regs + ETH_REG2);
 
 	/* Enable the internal phy */