igb: Avoid starting unnecessary workqueues

If ptp_clock_register() fails or CONFIG_PTP isn't enabled, avoid starting
PTP related workqueues.

In this way we can fix this:
 BUG: unable to handle page fault for address: ffffc9000440b6f8
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 100000067 P4D 100000067 PUD 1001e0067 PMD 107dc5067 PTE 0
 Oops: 0000 [#1] PREEMPT SMP
 [...]
 Workqueue: events igb_ptp_overflow_check
 RIP: 0010:igb_rd32+0x1f/0x60
 [...]
 Call Trace:
  igb_ptp_read_82580+0x20/0x50
  timecounter_read+0x15/0x60
  igb_ptp_overflow_check+0x1a/0x50
  process_one_work+0x1cb/0x3c0
  worker_thread+0x53/0x3f0
  ? rescuer_thread+0x370/0x370
  kthread+0x142/0x160
  ? kthread_associate_blkcg+0xc0/0xc0
  ret_from_fork+0x1f/0x30

Fixes: 1f6e817 ("igb: Prevent dropped Tx timestamps via work items and interrupts.")
Fixes: d339b13 ("igb: add PTP Hardware Clock code")
Signed-off-by: Alessio Igor Bogani <alessio.bogani@elettra.eu>
Tested-by: Arpana Arland <arpanax.arland@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230821171927.2203644-1-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: abogani

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

@@ -1385,18 +1385,6 @@ void igb_ptp_init(struct igb_adapter *adapter)
 		return;
 	}
 
-	spin_lock_init(&adapter->tmreg_lock);
-	INIT_WORK(&adapter->ptp_tx_work, igb_ptp_tx_work);
-
-	if (adapter->ptp_flags & IGB_PTP_OVERFLOW_CHECK)
-		INIT_DELAYED_WORK(&adapter->ptp_overflow_work,
-				  igb_ptp_overflow_check);
-
-	adapter->tstamp_config.rx_filter = HWTSTAMP_FILTER_NONE;
-	adapter->tstamp_config.tx_type = HWTSTAMP_TX_OFF;
-
-	igb_ptp_reset(adapter);
-
 	adapter->ptp_clock = ptp_clock_register(&adapter->ptp_caps,
 						&adapter->pdev->dev);
 	if (IS_ERR(adapter->ptp_clock)) {
@@ -1406,6 +1394,18 @@ void igb_ptp_init(struct igb_adapter *adapter)
 		dev_info(&adapter->pdev->dev, "added PHC on %s\n",
 			 adapter->netdev->name);
 		adapter->ptp_flags |= IGB_PTP_ENABLED;
+
+		spin_lock_init(&adapter->tmreg_lock);
+		INIT_WORK(&adapter->ptp_tx_work, igb_ptp_tx_work);
+
+		if (adapter->ptp_flags & IGB_PTP_OVERFLOW_CHECK)
+			INIT_DELAYED_WORK(&adapter->ptp_overflow_work,
+					  igb_ptp_overflow_check);
+
+		adapter->tstamp_config.rx_filter = HWTSTAMP_FILTER_NONE;
+		adapter->tstamp_config.tx_type = HWTSTAMP_TX_OFF;
+
+		igb_ptp_reset(adapter);
 	}
 }