net: ena: fix incorrect update of intr_delay_resolution

BugLink: https://bugs.launchpad.net/bugs/1853180

ena_dev->intr_moder_rx/tx_interval save the intervals received from the
user after dividing them by ena_dev->intr_delay_resolution. Therefore
when intr_delay_resolution changes, the code needs to first mutiply
intr_moder_rx/tx_interval by the previous intr_delay_resolution to get
the value originally given by the user, and only then divide it by the
new intr_delay_resolution.

Current code does not first multiply intr_moder_rx/tx_interval by the old
intr_delay_resolution. This commit fixes it.

Also initialize ena_dev->intr_delay_resolution to be 1.
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 79226cea)
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Khaled Elmously <khalid.elmously@canonical.com>
Acked-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/net/ethernet/amazon/ena/ena_com.c

@@ -1281,17 +1281,30 @@ static int ena_com_ind_tbl_convert_from_device(struct ena_com_dev *ena_dev)
 static void ena_com_update_intr_delay_resolution(struct ena_com_dev *ena_dev,
 						 u16 intr_delay_resolution)
 {
+	/* Initial value of intr_delay_resolution might be 0 */
+	u16 prev_intr_delay_resolution =
+		ena_dev->intr_delay_resolution ?
+		ena_dev->intr_delay_resolution :
+		ENA_DEFAULT_INTR_DELAY_RESOLUTION;
+
 	if (!intr_delay_resolution) {
 		pr_err("Illegal intr_delay_resolution provided. Going to use default 1 usec resolution\n");
-		intr_delay_resolution = 1;
+		intr_delay_resolution = ENA_DEFAULT_INTR_DELAY_RESOLUTION;
 	}
-	ena_dev->intr_delay_resolution = intr_delay_resolution;
 
 	/* update Rx */
-	ena_dev->intr_moder_rx_interval /= intr_delay_resolution;
+	ena_dev->intr_moder_rx_interval =
+		ena_dev->intr_moder_rx_interval *
+		prev_intr_delay_resolution /
+		intr_delay_resolution;
 
 	/* update Tx */
-	ena_dev->intr_moder_tx_interval /= intr_delay_resolution;
+	ena_dev->intr_moder_tx_interval =
+		ena_dev->intr_moder_tx_interval *
+		prev_intr_delay_resolution /
+		intr_delay_resolution;
+
+	ena_dev->intr_delay_resolution = intr_delay_resolution;
 }
 
 /*****************************************************************************/

drivers/net/ethernet/amazon/ena/ena_com.h

@@ -74,6 +74,7 @@
 
 #define ENA_INTR_INITIAL_TX_INTERVAL_USECS		196
 #define ENA_INTR_INITIAL_RX_INTERVAL_USECS		0
+#define ENA_DEFAULT_INTR_DELAY_RESOLUTION		1
 
 #define ENA_HW_HINTS_NO_TIMEOUT				0xFFFF
 

drivers/net/ethernet/amazon/ena/ena_netdev.c

@@ -3501,6 +3501,7 @@ static int ena_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	*/
 	ena_dev->intr_moder_tx_interval = ENA_INTR_INITIAL_TX_INTERVAL_USECS;
 	ena_dev->intr_moder_rx_interval = ENA_INTR_INITIAL_RX_INTERVAL_USECS;
+	ena_dev->intr_delay_resolution = ENA_DEFAULT_INTR_DELAY_RESOLUTION;
 	io_queue_num = ena_calc_io_queue_num(pdev, ena_dev, &get_feat_ctx);
 	rc = ena_calc_queue_size(&calc_queue_ctx);
 	if (rc || io_queue_num <= 0) {