net: axienet: set mdio clock according to bus-frequency

Some FPGA platforms have 80KHz MDIO bus frequency constraint when
connecting Ethernet to its on-board external Marvell PHY. Thus, we may
have to set MDIO clock according to the DT. Otherwise, use the default
2.5 MHz, as specified by 802.3, if the entry is not present.

Also, change MAX_MDIO_FREQ to DEFAULT_MDIO_FREQ because we may actually
set MDIO bus frequency higher than 2.5MHz if undelying devices support
it. And properly disable the mdio bus clock in error path.
Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/xilinx/xilinx_axienet_mdio.c

@@ -17,7 +17,7 @@
 
 #include "xilinx_axienet.h"
 
-#define MAX_MDIO_FREQ		2500000 /* 2.5 MHz */
+#define DEFAULT_MDIO_FREQ	2500000 /* 2.5 MHz */
 #define DEFAULT_HOST_CLOCK	150000000 /* 150 MHz */
 
 /* Wait till MDIO interface is ready to accept a new transaction.*/
@@ -147,15 +147,20 @@ static int axienet_mdio_write(struct mii_bus *bus, int phy_id, int reg,
 /**
  * axienet_mdio_enable - MDIO hardware setup function
  * @lp:		Pointer to axienet local data structure.
+ * @np:		Pointer to mdio device tree node.
  *
- * Return:	0 on success, -ETIMEDOUT on a timeout.
+ * Return:	0 on success, -ETIMEDOUT on a timeout, -EOVERFLOW on a clock
+ *		divisor overflow.
  *
  * Sets up the MDIO interface by initializing the MDIO clock and enabling the
  * MDIO interface in hardware.
  **/
-static int axienet_mdio_enable(struct axienet_local *lp)
+static int axienet_mdio_enable(struct axienet_local *lp, struct device_node *np)
 {
+	u32 mdio_freq = DEFAULT_MDIO_FREQ;
 	u32 host_clock;
+	u32 clk_div;
+	int ret;
 
 	lp->mii_clk_div = 0;
 
@@ -184,6 +189,12 @@ static int axienet_mdio_enable(struct axienet_local *lp)
 			    host_clock);
 	}
 
+	if (np)
+		of_property_read_u32(np, "clock-frequency", &mdio_freq);
+	if (mdio_freq != DEFAULT_MDIO_FREQ)
+		netdev_info(lp->ndev, "Setting non-standard mdio bus frequency to %u Hz\n",
+			    mdio_freq);
+
 	/* clk_div can be calculated by deriving it from the equation:
 	 * fMDIO = fHOST / ((1 + clk_div) * 2)
 	 *
@@ -209,29 +220,42 @@ static int axienet_mdio_enable(struct axienet_local *lp)
 	 * "clock-frequency" from the CPU
 	 */
 
-	lp->mii_clk_div = (host_clock / (MAX_MDIO_FREQ * 2)) - 1;
+	clk_div = (host_clock / (mdio_freq * 2)) - 1;
 	/* If there is any remainder from the division of
-	 * fHOST / (MAX_MDIO_FREQ * 2), then we need to add
-	 * 1 to the clock divisor or we will surely be above 2.5 MHz
+	 * fHOST / (mdio_freq * 2), then we need to add
+	 * 1 to the clock divisor or we will surely be
+	 * above the requested frequency
 	 */
-	if (host_clock % (MAX_MDIO_FREQ * 2))
-		lp->mii_clk_div++;
+	if (host_clock % (mdio_freq * 2))
+		clk_div++;
+
+	/* Check for overflow of mii_clk_div */
+	if (clk_div & ~XAE_MDIO_MC_CLOCK_DIVIDE_MAX) {
+		netdev_warn(lp->ndev, "MDIO clock divisor overflow\n");
+		return -EOVERFLOW;
+	}
+	lp->mii_clk_div = (u8)clk_div;
 
 	netdev_dbg(lp->ndev,
 		   "Setting MDIO clock divisor to %u/%u Hz host clock.\n",
 		   lp->mii_clk_div, host_clock);
 
-	axienet_iow(lp, XAE_MDIO_MC_OFFSET, lp->mii_clk_div | XAE_MDIO_MC_MDIOEN_MASK);
+	axienet_mdio_mdc_enable(lp);
 
-	return axienet_mdio_wait_until_ready(lp);
+	ret = axienet_mdio_wait_until_ready(lp);
+	if (ret)
+		axienet_mdio_mdc_disable(lp);
+
+	return ret;
 }
 
 /**
  * axienet_mdio_setup - MDIO setup function
  * @lp:		Pointer to axienet local data structure.
  *
- * Return:	0 on success, -ETIMEDOUT on a timeout, -ENOMEM when
- *		mdiobus_alloc (to allocate memory for mii bus structure) fails.
+ * Return:	0 on success, -ETIMEDOUT on a timeout, -EOVERFLOW on a clock
+ *		divisor overflow, -ENOMEM when mdiobus_alloc (to allocate
+ *		memory for mii bus structure) fails.
  *
  * Sets up the MDIO interface by initializing the MDIO clock.
  * Register the MDIO interface.
@@ -242,10 +266,6 @@ int axienet_mdio_setup(struct axienet_local *lp)
 	struct mii_bus *bus;
 	int ret;
 
-	ret = axienet_mdio_enable(lp);
-	if (ret < 0)
-		return ret;
-
 	bus = mdiobus_alloc();
 	if (!bus)
 		return -ENOMEM;
@@ -261,15 +281,23 @@ int axienet_mdio_setup(struct axienet_local *lp)
 	lp->mii_bus = bus;
 
 	mdio_node = of_get_child_by_name(lp->dev->of_node, "mdio");
+	ret = axienet_mdio_enable(lp, mdio_node);
+	if (ret < 0)
+		goto unregister;
 	ret = of_mdiobus_register(bus, mdio_node);
+	if (ret)
+		goto unregister_mdio_enabled;
+	of_node_put(mdio_node);
+	axienet_mdio_mdc_disable(lp);
+	return 0;
+
+unregister_mdio_enabled:
+	axienet_mdio_mdc_disable(lp);
+unregister:
 	of_node_put(mdio_node);
-	if (ret) {
 	mdiobus_free(bus);
 	lp->mii_bus = NULL;
 	return ret;
-	}
-	axienet_mdio_mdc_disable(lp);
-	return 0;
 }
 
 /**