igb: conditionalize I2C bit banging on external thermal sensor support

Commit a97f8783 ("igb: unbreak I2C bit-banging on i350") introduced
code to change I2C settings to bit banging unconditionally.

However, this patch introduced a regression:  On an Intel S2600CWR
Server Board with three NICs:

- 1x dual-port copper
  Intel I350 Gigabit Network Connection [8086:1521] (rev 01)
  fw 1.63, 0x80000dda

- 2x quad-port SFP+ with copper SFP Avago ABCU-5700RZ
  Intel I350 Gigabit Fiber Network Connection [8086:1522] (rev 01)
  fw 1.52.0

the SFP NICs no longer get link at all.  Reverting commit a97f8783
or switching to the Intel out-of-tree driver both fix the problem.

Per the igb out-of-tree driver, I2C bit banging on i350 depends on
support for an external thermal sensor (ETS).  However, commit
a97f8783 added bit banging unconditionally.  Additionally, the
out-of-tree driver always calls init_thermal_sensor_thresh on probe,
while our driver only calls init_thermal_sensor_thresh only in
igb_reset(), and only if an ETS is present, ignoring the internal
thermal sensor.  The affected SFPs don't provide an ETS.  Per Intel,
the behaviour is a result of i350 firmware requirements.

This patch fixes the problem by aligning the behaviour to the
out-of-tree driver:

- split igb_init_i2c() into two functions:
  - igb_init_i2c() only performs the basic I2C initialization.
  - igb_set_i2c_bb() makes sure that E1000_CTRL_I2C_ENA is set
    and enables bit-banging.

- igb_probe() only calls igb_set_i2c_bb() if an ETS is present.

- igb_probe() calls init_thermal_sensor_thresh() unconditionally.

- igb_reset() aligns its behaviour to igb_probe(), i. e., call
  igb_set_i2c_bb() if an ETS is present and call
  init_thermal_sensor_thresh() unconditionally.

Fixes: a97f8783 ("igb: unbreak I2C bit-banging on i350")
Tested-by: Mateusz Palczewski <mateusz.palczewski@intel.com>
Co-developed-by: Jamie Bainbridge <jbainbri@redhat.com>
Signed-off-by: Jamie Bainbridge <jbainbri@redhat.com>
Signed-off-by: Corinna Vinschen <vinschen@redhat.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://lore.kernel.org/r/20230214185549.1306522-1-anthony.l.nguyen@intel.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -2256,6 +2256,30 @@ static void igb_enable_mas(struct igb_adapter *adapter)
 	}
 }
 
+#ifdef CONFIG_IGB_HWMON
+/**
+ *  igb_set_i2c_bb - Init I2C interface
+ *  @hw: pointer to hardware structure
+ **/
+static void igb_set_i2c_bb(struct e1000_hw *hw)
+{
+	u32 ctrl_ext;
+	s32 i2cctl;
+
+	ctrl_ext = rd32(E1000_CTRL_EXT);
+	ctrl_ext |= E1000_CTRL_I2C_ENA;
+	wr32(E1000_CTRL_EXT, ctrl_ext);
+	wrfl();
+
+	i2cctl = rd32(E1000_I2CPARAMS);
+	i2cctl |= E1000_I2CBB_EN
+		| E1000_I2C_CLK_OE_N
+		| E1000_I2C_DATA_OE_N;
+	wr32(E1000_I2CPARAMS, i2cctl);
+	wrfl();
+}
+#endif
+
 void igb_reset(struct igb_adapter *adapter)
 {
 	struct pci_dev *pdev = adapter->pdev;
@@ -2400,6 +2424,7 @@ void igb_reset(struct igb_adapter *adapter)
 			 * interface.
 			 */
 			if (adapter->ets)
+				igb_set_i2c_bb(hw);
 			mac->ops.init_thermal_sensor_thresh(hw);
 		}
 	}
@@ -3117,21 +3142,12 @@ static void igb_init_mas(struct igb_adapter *adapter)
  **/
 static s32 igb_init_i2c(struct igb_adapter *adapter)
 {
-	struct e1000_hw *hw = &adapter->hw;
 	s32 status = 0;
-	s32 i2cctl;
 
 	/* I2C interface supported on i350 devices */
 	if (adapter->hw.mac.type != e1000_i350)
 		return 0;
 
-	i2cctl = rd32(E1000_I2CPARAMS);
-	i2cctl |= E1000_I2CBB_EN
-		| E1000_I2C_CLK_OUT | E1000_I2C_CLK_OE_N
-		| E1000_I2C_DATA_OUT | E1000_I2C_DATA_OE_N;
-	wr32(E1000_I2CPARAMS, i2cctl);
-	wrfl();
-
 	/* Initialize the i2c bus which is controlled by the registers.
 	 * This bus will use the i2c_algo_bit structure that implements
 	 * the protocol through toggling of the 4 bits in the register.
@@ -3521,6 +3537,12 @@ static int igb_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 			adapter->ets = true;
 		else
 			adapter->ets = false;
+		/* Only enable I2C bit banging if an external thermal
+		 * sensor is supported.
+		 */
+		if (adapter->ets)
+			igb_set_i2c_bb(hw);
+		hw->mac.ops.init_thermal_sensor_thresh(hw);
 		if (igb_sysfs_init(adapter))
 			dev_err(&pdev->dev,
 				"failed to allocate sysfs resources\n");