i40e: stop using cmpxchg flow in i40e_set_priv_flags()

Now that the only places which modify flags are either (a) during
initialization prior to creating a netdevice, or (b) while holding the
rtnl lock, we no longer need the cmpxchg64 call in i40e_set_priv_flags.
Signed-off-by: NJacob Keller <jacob.e.keller@intel.com>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_ethtool.c

@@ -4436,21 +4436,12 @@ static int i40e_set_priv_flags(struct net_device *dev, u32 flags)
 		}
 	}
 
-	/* Compare and exchange the new flags into place. If we failed, that
-	 * is if cmpxchg returns anything but the old value, this means that
-	 * something else has modified the flags variable since we copied it
-	 * originally. We'll just punt with an error and log something in the
-	 * message buffer.
-	 *
-	 * This is the point of no return for this function.  We need to have
-	 * checked any discrepancies or misconfigurations and returned
-	 * EOPNOTSUPP before updating pf->flags here.
+	/* Now that we've checked to ensure that the new flags are valid, load
+	 * them into place. Since we only modify flags either (a) during
+	 * initialization or (b) while holding the RTNL lock, we don't need
+	 * anything fancy here.
 	 */
-	if (cmpxchg64(&pf->flags, orig_flags, new_flags) != orig_flags) {
-		dev_warn(&pf->pdev->dev,
-			 "Unable to update pf->flags as it was modified by another thread...\n");
-		return -EAGAIN;
-	}
+	pf->flags = new_flags;
 
 	/* Process any additional changes needed as a result of flag changes.
 	 * The changed_flags value reflects the list of bits that were