net: ena: reduce driver load time

This commit reduces the driver load time by using usec resolution
instead of msec when polling for hardware state change.

Also add back-off mechanism to handle cases where minimal sleep
time is not enough.
Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -62,7 +62,9 @@
 
 #define ENA_REGS_ADMIN_INTR_MASK 1
 
-#define ENA_POLL_MS	5
+#define ENA_MIN_ADMIN_POLL_US 100
+
+#define ENA_MAX_ADMIN_POLL_US 5000
 
 /*****************************************************************************/
 /*****************************************************************************/
@@ -540,12 +542,20 @@ static int ena_com_comp_status_to_errno(u8 comp_status)
 	return -EINVAL;
 }
 
+static void ena_delay_exponential_backoff_us(u32 exp, u32 delay_us)
+{
+	delay_us = max_t(u32, ENA_MIN_ADMIN_POLL_US, delay_us);
+	delay_us = min_t(u32, delay_us * (1U << exp), ENA_MAX_ADMIN_POLL_US);
+	usleep_range(delay_us, 2 * delay_us);
+}
+
 static int ena_com_wait_and_process_admin_cq_polling(struct ena_comp_ctx *comp_ctx,
 						     struct ena_com_admin_queue *admin_queue)
 {
 	unsigned long flags = 0;
 	unsigned long timeout;
 	int ret;
+	u32 exp = 0;
 
 	timeout = jiffies + usecs_to_jiffies(admin_queue->completion_timeout);
 
@@ -569,7 +579,8 @@ static int ena_com_wait_and_process_admin_cq_polling(struct ena_comp_ctx *comp_c
 			goto err;
 		}
 
-		msleep(ENA_POLL_MS);
+		ena_delay_exponential_backoff_us(exp++,
+						 admin_queue->ena_dev->ena_min_poll_delay_us);
 	}
 
 	if (unlikely(comp_ctx->status == ENA_CMD_ABORTED)) {
@@ -939,12 +950,13 @@ static void ena_com_io_queue_free(struct ena_com_dev *ena_dev,
 static int wait_for_reset_state(struct ena_com_dev *ena_dev, u32 timeout,
 				u16 exp_state)
 {
-	u32 val, i;
+	u32 val, exp = 0;
+	unsigned long timeout_stamp;
 
-	/* Convert timeout from resolution of 100ms to ENA_POLL_MS */
-	timeout = (timeout * 100) / ENA_POLL_MS;
+	/* Convert timeout from resolution of 100ms to us resolution. */
+	timeout_stamp = jiffies + usecs_to_jiffies(100 * 1000 * timeout);
 
-	for (i = 0; i < timeout; i++) {
+	while (1) {
 		val = ena_com_reg_bar_read32(ena_dev, ENA_REGS_DEV_STS_OFF);
 
 		if (unlikely(val == ENA_MMIO_READ_TIMEOUT)) {
@@ -956,10 +968,11 @@ static int wait_for_reset_state(struct ena_com_dev *ena_dev, u32 timeout,
 			exp_state)
 			return 0;
 
-		msleep(ENA_POLL_MS);
-	}
+		if (time_is_before_jiffies(timeout_stamp))
+			return -ETIME;
 
-	return -ETIME;
+		ena_delay_exponential_backoff_us(exp++, ena_dev->ena_min_poll_delay_us);
+	}
 }
 
 static bool ena_com_check_supported_feature_id(struct ena_com_dev *ena_dev,
@@ -1436,11 +1449,13 @@ void ena_com_wait_for_abort_completion(struct ena_com_dev *ena_dev)
 {
 	struct ena_com_admin_queue *admin_queue = &ena_dev->admin_queue;
 	unsigned long flags = 0;
+	u32 exp = 0;
 
 	spin_lock_irqsave(&admin_queue->q_lock, flags);
 	while (atomic_read(&admin_queue->outstanding_cmds) != 0) {
 		spin_unlock_irqrestore(&admin_queue->q_lock, flags);
-		msleep(ENA_POLL_MS);
+		ena_delay_exponential_backoff_us(exp++,
+						 ena_dev->ena_min_poll_delay_us);
 		spin_lock_irqsave(&admin_queue->q_lock, flags);
 	}
 	spin_unlock_irqrestore(&admin_queue->q_lock, flags);
@@ -1788,6 +1803,7 @@ int ena_com_admin_init(struct ena_com_dev *ena_dev,
 	if (ret)
 		goto error;
 
+	admin_queue->ena_dev = ena_dev;
 	admin_queue->running_state = true;
 
 	return 0;

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

@@ -239,6 +239,7 @@ struct ena_com_stats_admin {
 
 struct ena_com_admin_queue {
 	void *q_dmadev;
+	struct ena_com_dev *ena_dev;
 	spinlock_t q_lock; /* spinlock for the admin queue */
 
 	struct ena_comp_ctx *comp_ctx;
@@ -351,6 +352,8 @@ struct ena_com_dev {
 	struct ena_intr_moder_entry *intr_moder_tbl;
 
 	struct ena_com_llq_info llq_info;
+
+	u32 ena_min_poll_delay_us;
 };
 
 struct ena_com_dev_get_features_ctx {

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

@@ -4166,6 +4166,8 @@ static int ena_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 		goto err_free_region;
 	}
 
+	ena_dev->ena_min_poll_delay_us = ENA_ADMIN_POLL_DELAY_US;
+
 	ena_dev->dmadev = &pdev->dev;
 
 	rc = ena_device_init(ena_dev, pdev, &get_feat_ctx, &wd_state);

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

@@ -129,6 +129,8 @@
 #define ENA_IO_IRQ_FIRST_IDX		1
 #define ENA_IO_IRQ_IDX(q)		(ENA_IO_IRQ_FIRST_IDX + (q))
 
+#define ENA_ADMIN_POLL_DELAY_US 100
+
 /* ENA device should send keep alive msg every 1 sec.
  * We wait for 6 sec just to be on the safe side.
  */