i40e: Fix kernel panic on enable/disable LLDP

If DCB is configured on the link partner switch with an
unsupported traffic class configuration (e.g. non-contiguous TCs),
the driver is flagging DCB as disabled.  But, for future DCB
LLDPDUs, the driver was checking if the interface was DCB capable
instead of enabled.  This was causing a kernel panic when LLDP
was enabled/disabled on the link partner switch.

This patch corrects the situation by having the LLDP event handler
check the correct flag in the pf structure.  It also cleans up the
setting and clearing of the enabled flag for other checks.

Signed-off-by: Dave Ertman <david.m.ertman@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
index 828ed28..d0b3a1b 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_main.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
@@ -5113,9 +5113,13 @@
 				       DCB_CAP_DCBX_VER_IEEE;
 
 			pf->flags |= I40E_FLAG_DCB_CAPABLE;
-			/* Enable DCB tagging only when more than one TC */
+			/* Enable DCB tagging only when more than one TC
+			 * or explicitly disable if only one TC
+			 */
 			if (i40e_dcb_get_num_tc(&hw->local_dcbx_config) > 1)
 				pf->flags |= I40E_FLAG_DCB_ENABLED;
+			else
+				pf->flags &= ~I40E_FLAG_DCB_ENABLED;
 			dev_dbg(&pf->pdev->dev,
 				"DCBX offload is supported for this PF.\n");
 		}
@@ -5716,7 +5720,7 @@
 	u8 type;
 
 	/* Not DCB capable or capability disabled */
-	if (!(pf->flags & I40E_FLAG_DCB_CAPABLE))
+	if (!(pf->flags & I40E_FLAG_DCB_ENABLED))
 		return ret;
 
 	/* Ignore if event is not for Nearest Bridge */
@@ -7896,6 +7900,7 @@
 #endif
 				       I40E_FLAG_RSS_ENABLED	|
 				       I40E_FLAG_DCB_CAPABLE	|
+				       I40E_FLAG_DCB_ENABLED	|
 				       I40E_FLAG_SRIOV_ENABLED	|
 				       I40E_FLAG_FD_SB_ENABLED	|
 				       I40E_FLAG_FD_ATR_ENABLED	|
@@ -10502,6 +10507,7 @@
 			       I40E_FLAG_FD_SB_ENABLED	|
 			       I40E_FLAG_FD_ATR_ENABLED	|
 			       I40E_FLAG_DCB_CAPABLE	|
+			       I40E_FLAG_DCB_ENABLED	|
 			       I40E_FLAG_SRIOV_ENABLED	|
 			       I40E_FLAG_VMDQ_ENABLED);
 	} else if (!(pf->flags & (I40E_FLAG_RSS_ENABLED |
@@ -10525,7 +10531,8 @@
 		/* Not enough queues for all TCs */
 		if ((pf->flags & I40E_FLAG_DCB_CAPABLE) &&
 		    (queues_left < I40E_MAX_TRAFFIC_CLASS)) {
-			pf->flags &= ~I40E_FLAG_DCB_CAPABLE;
+			pf->flags &= ~(I40E_FLAG_DCB_CAPABLE |
+					I40E_FLAG_DCB_ENABLED);
 			dev_info(&pf->pdev->dev, "not enough queues for DCB. DCB is disabled.\n");
 		}
 		pf->num_lan_qps = max_t(int, pf->rss_size_max,
@@ -10922,7 +10929,7 @@
 	err = i40e_init_pf_dcb(pf);
 	if (err) {
 		dev_info(&pdev->dev, "DCB init failed %d, disabled\n", err);
-		pf->flags &= ~I40E_FLAG_DCB_CAPABLE;
+		pf->flags &= ~(I40E_FLAG_DCB_CAPABLE & I40E_FLAG_DCB_ENABLED);
 		/* Continue without DCB enabled */
 	}
 #endif /* CONFIG_I40E_DCB */