iavf: validate tx_coalesce_usecs even if rx_coalesce_usecs is zero

In __iavf_set_coalesce, the driver checks both ec->rx_coalesce_usecs and
ec->tx_coalesce_usecs for validity. It does this via a chain if if/else-if
blocks. If every single branch of the series of if statements exited, this
would be fine. However, the rx_coalesce_usecs is checked against zero to
print an informative message if use_adaptive_rx_coalesce is enabled. If
this check is true, it short circuits the entire chain of statements,
preventing validation of the tx_coalesce_usecs field.

Indeed, since commit e792779e ("iavf: Prevent changing static ITR
values if adaptive moderation is on") the iavf driver actually rejects any
change to the tx_coalesce_usecs or rx_coalesce_usecs when
use_adaptive_tx_coalesce or use_adaptive_rx_coalesce is enabled, making
this checking a bit redundant.

Fix this error by removing the unnecessary and redundant checks for
use_adaptive_rx_coalesce and use_adaptive_tx_coalesce. Since zero is a
valid value, and since the tx_coalesce_usecs and rx_coalesce_usecs fields
are already unsigned, remove the minimum value check. This allows assigning
an ITR value ranging from 0-8160 as described by the printed message.

Fixes: 65e87c03 ("i40evf: support queue-specific settings for interrupt moderation")
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/iavf/iavf_ethtool.c

@@ -827,18 +827,10 @@ static int __iavf_set_coalesce(struct net_device *netdev,
 	struct iavf_adapter *adapter = netdev_priv(netdev);
 	int i;
 
-	if (ec->rx_coalesce_usecs == 0) {
-		if (ec->use_adaptive_rx_coalesce)
-			netif_info(adapter, drv, netdev, "rx-usecs=0, need to disable adaptive-rx for a complete disable\n");
-	} else if ((ec->rx_coalesce_usecs < IAVF_MIN_ITR) ||
-		   (ec->rx_coalesce_usecs > IAVF_MAX_ITR)) {
+	if (ec->rx_coalesce_usecs > IAVF_MAX_ITR) {
 		netif_info(adapter, drv, netdev, "Invalid value, rx-usecs range is 0-8160\n");
 		return -EINVAL;
-	} else if (ec->tx_coalesce_usecs == 0) {
-		if (ec->use_adaptive_tx_coalesce)
-			netif_info(adapter, drv, netdev, "tx-usecs=0, need to disable adaptive-tx for a complete disable\n");
-	} else if ((ec->tx_coalesce_usecs < IAVF_MIN_ITR) ||
-		   (ec->tx_coalesce_usecs > IAVF_MAX_ITR)) {
+	} else if (ec->tx_coalesce_usecs > IAVF_MAX_ITR) {
 		netif_info(adapter, drv, netdev, "Invalid value, tx-usecs range is 0-8160\n");
 		return -EINVAL;
 	}

drivers/net/ethernet/intel/iavf/iavf_txrx.h

@@ -15,7 +15,6 @@
  */
 #define IAVF_ITR_DYNAMIC	0x8000	/* use top bit as a flag */
 #define IAVF_ITR_MASK		0x1FFE	/* mask for ITR register value */
-#define IAVF_MIN_ITR		     2	/* reg uses 2 usec resolution */
 #define IAVF_ITR_100K		    10	/* all values below must be even */
 #define IAVF_ITR_50K		    20
 #define IAVF_ITR_20K		    50