[PATCH] net: memac_phy: add a timeout to MDIO operations

[Ioana Ciornei]

We have encountered circumstances when a board design does not include
pull-up resistors on the external MDIO buses which are not used. This
leads to the MDIO data line not being pulled-up, thus the MDIO controller
will always see the line as busy.

Without a timeout in the MDIO bus driver, the execution is stuck in an
infinite loop when any access is initiated on that external bus.

Add a timeout in the driver so that we are protected in this
circumstance. This is similar to what is being done in the Linux
xgmac_mdio driver.

Signed-off-by: Ioana Ciornei <ioana.ciornei at nxp.com>
---
 drivers/net/fm/memac_phy.c | 76 +++++++++++++++++++++++++++++---------
 1 file changed, 58 insertions(+), 18 deletions(-)

diff --git a/drivers/net/fm/memac_phy.c b/drivers/net/fm/memac_phy.c
index c2ef1b4e737e..b92a012ce79f 100644
--- a/drivers/net/fm/memac_phy.c
+++ b/drivers/net/fm/memac_phy.c
@@ -22,6 +22,8 @@
 #define memac_setbits_32(a, v)	setbits_be32(a, v)
 #endif
 
+#define MAX_NUM_RETRIES		1000
+
 static u32 memac_in_32(u32 *reg)
 {
 #ifdef CONFIG_SYS_MEMAC_LITTLE_ENDIAN
@@ -31,6 +33,42 @@ static u32 memac_in_32(u32 *reg)
 #endif
 }
 
+/*
+ * Wait until the MDIO bus is free
+ */
+static int memac_wait_until_free(struct memac_mdio_controller *regs)
+{
+	unsigned int timeout = MAX_NUM_RETRIES;
+
+	while ((memac_in_32(&regs->mdio_stat) & MDIO_STAT_BSY) && timeout--)
+		;
+
+	if (!timeout) {
+		printf("timeout waiting for MDIO bus to be free\n");
+		return -ETIMEDOUT;
+	}
+
+	return 0;
+}
+
+/*
+ * Wait till the MDIO read or write operation is complete
+ */
+static int memac_wait_until_done(struct memac_mdio_controller *regs)
+{
+	unsigned int timeout = MAX_NUM_RETRIES;
+
+	while ((memac_in_32(&regs->mdio_data) & MDIO_DATA_BSY) && timeout--)
+		;
+
+	if (!timeout) {
+		printf("timeout waiting for MDIO operation to complete\n");
+		return -ETIMEDOUT;
+	}
+
+	return 0;
+}
+
 /*
  * Write value to the PHY for this device to the register at regnum, waiting
  * until the write is done before it returns.  All PHY configuration has to be
@@ -42,6 +80,7 @@ int memac_mdio_write(struct mii_dev *bus, int port_addr, int dev_addr,
 	u32 mdio_ctl;
 	struct memac_mdio_controller *regs = bus->priv;
 	u32 c45 = 1; /* Default to 10G interface */
+	int err;
 
 	if (dev_addr == MDIO_DEVAD_NONE) {
 		c45 = 0; /* clause 22 */
@@ -50,9 +89,9 @@ int memac_mdio_write(struct mii_dev *bus, int port_addr, int dev_addr,
 	} else
 		memac_setbits_32(&regs->mdio_stat, MDIO_STAT_ENC);
 
-	/* Wait till the bus is free */
-	while ((memac_in_32(&regs->mdio_stat)) & MDIO_STAT_BSY)
-		;
+	err = memac_wait_until_free(regs);
+	if (err)
+		return err;
 
 	/* Set the port and dev addr */
 	mdio_ctl = MDIO_CTL_PORT_ADDR(port_addr) | MDIO_CTL_DEV_ADDR(dev_addr);
@@ -62,16 +101,16 @@ int memac_mdio_write(struct mii_dev *bus, int port_addr, int dev_addr,
 	if (c45)
 		memac_out_32(&regs->mdio_addr, regnum & 0xffff);
 
-	/* Wait till the bus is free */
-	while ((memac_in_32(&regs->mdio_stat)) & MDIO_STAT_BSY)
-		;
+	err = memac_wait_until_free(regs);
+	if (err)
+		return err;
 
 	/* Write the value to the register */
 	memac_out_32(&regs->mdio_data, MDIO_DATA(value));
 
-	/* Wait till the MDIO write is complete */
-	while ((memac_in_32(&regs->mdio_data)) & MDIO_DATA_BSY)
-		;
+	err = memac_wait_until_done(regs);
+	if (err)
+		return err;
 
 	return 0;
 }
@@ -87,6 +126,7 @@ int memac_mdio_read(struct mii_dev *bus, int port_addr, int dev_addr,
 	u32 mdio_ctl;
 	struct memac_mdio_controller *regs = bus->priv;
 	u32 c45 = 1;
+	int err;
 
 	if (dev_addr == MDIO_DEVAD_NONE) {
 		if (!strcmp(bus->name, DEFAULT_FM_TGEC_MDIO_NAME))
@@ -97,9 +137,9 @@ int memac_mdio_read(struct mii_dev *bus, int port_addr, int dev_addr,
 	} else
 		memac_setbits_32(&regs->mdio_stat, MDIO_STAT_ENC);
 
-	/* Wait till the bus is free */
-	while ((memac_in_32(&regs->mdio_stat)) & MDIO_STAT_BSY)
-		;
+	err = memac_wait_until_free(regs);
+	if (err)
+		return err;
 
 	/* Set the Port and Device Addrs */
 	mdio_ctl = MDIO_CTL_PORT_ADDR(port_addr) | MDIO_CTL_DEV_ADDR(dev_addr);
@@ -109,17 +149,17 @@ int memac_mdio_read(struct mii_dev *bus, int port_addr, int dev_addr,
 	if (c45)
 		memac_out_32(&regs->mdio_addr, regnum & 0xffff);
 
-	/* Wait till the bus is free */
-	while ((memac_in_32(&regs->mdio_stat)) & MDIO_STAT_BSY)
-		;
+	err = memac_wait_until_free(regs);
+	if (err)
+		return err;
 
 	/* Initiate the read */
 	mdio_ctl |= MDIO_CTL_READ;
 	memac_out_32(&regs->mdio_ctl, mdio_ctl);
 
-	/* Wait till the MDIO write is complete */
-	while ((memac_in_32(&regs->mdio_data)) & MDIO_DATA_BSY)
-		;
+	err = memac_wait_until_done(regs);
+	if (err)
+		return err;
 
 	/* Return all Fs if nothing was there */
 	if (memac_in_32(&regs->mdio_stat) & MDIO_STAT_RD_ER)
-- 
2.17.1