ixgbe: add I2C clock stretching

This patch adds support for I2C clock stretching which is required per
SFF-8636.  Customers with passive DA cables implement clock stretching
would fail without this patch.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c

@@ -1582,13 +1582,21 @@ static s32 ixgbe_clock_out_i2c_bit(struct ixgbe_hw *hw, bool data)
  **/
 static void ixgbe_raise_i2c_clk(struct ixgbe_hw *hw, u32 *i2cctl)
 {
-	*i2cctl |= IXGBE_I2C_CLK_OUT;
-
-	IXGBE_WRITE_REG(hw, IXGBE_I2CCTL, *i2cctl);
-	IXGBE_WRITE_FLUSH(hw);
+	u32 i = 0;
+	u32 timeout = IXGBE_I2C_CLOCK_STRETCHING_TIMEOUT;
+	u32 i2cctl_r = 0;
 
-	/* SCL rise time (1000ns) */
-	udelay(IXGBE_I2C_T_RISE);
+	for (i = 0; i < timeout; i++) {
+		*i2cctl |= IXGBE_I2C_CLK_OUT;
+		IXGBE_WRITE_REG(hw, IXGBE_I2CCTL, *i2cctl);
+		IXGBE_WRITE_FLUSH(hw);
+		/* SCL rise time (1000ns) */
+		udelay(IXGBE_I2C_T_RISE);
+
+		i2cctl_r = IXGBE_READ_REG(hw, IXGBE_I2CCTL);
+		if (i2cctl_r & IXGBE_I2C_CLK_IN)
+			break;
+	}
 }
 
 /**

drivers/net/ethernet/intel/ixgbe/ixgbe_type.h

@@ -110,6 +110,7 @@
 #define IXGBE_I2C_CLK_OUT   0x00000002
 #define IXGBE_I2C_DATA_IN   0x00000004
 #define IXGBE_I2C_DATA_OUT  0x00000008
+#define IXGBE_I2C_CLOCK_STRETCHING_TIMEOUT	500
 
 /* Interrupt Registers */
 #define IXGBE_EICR      0x00800