sfc: Work-around flush timeout when flushes have completed

We sometimes hit a "failed to flush" timeout on some TX queues, but the
flushes have completed and the flush completion events seem to go missing.
In this case, we can check the TX_DESC_PTR_TBL register and drain the
queues if the flushes had finished.

[bwh: Minor fixes to coding style]
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/net_driver.h

@@ -200,6 +200,7 @@ struct efx_tx_queue {
 	/* Members shared between paths and sometimes updated */
 	unsigned int empty_read_count ____cacheline_aligned_in_smp;
 #define EFX_EMPTY_COUNT_VALID 0x80000000
+	atomic_t flush_outstanding;
 };
 
 /**

drivers/net/ethernet/sfc/nic.c

@@ -73,6 +73,8 @@
 	_EFX_CHANNEL_MAGIC(_EFX_CHANNEL_MAGIC_TX_DRAIN,			\
 			   (_tx_queue)->queue)
 
+static void efx_magic_event(struct efx_channel *channel, u32 magic);
+
 /**************************************************************************
  *
  * Solarstorm hardware access
@@ -491,6 +493,9 @@ static void efx_flush_tx_queue(struct efx_tx_queue *tx_queue)
 	struct efx_nic *efx = tx_queue->efx;
 	efx_oword_t tx_flush_descq;
 
+	WARN_ON(atomic_read(&tx_queue->flush_outstanding));
+	atomic_set(&tx_queue->flush_outstanding, 1);
+
 	EFX_POPULATE_OWORD_2(tx_flush_descq,
 			     FRF_AZ_TX_FLUSH_DESCQ_CMD, 1,
 			     FRF_AZ_TX_FLUSH_DESCQ, tx_queue->queue);
@@ -666,6 +671,47 @@ static bool efx_flush_wake(struct efx_nic *efx)
 		 && atomic_read(&efx->rxq_flush_pending) > 0));
 }
 
+static bool efx_check_tx_flush_complete(struct efx_nic *efx)
+{
+	bool i = true;
+	efx_oword_t txd_ptr_tbl;
+	struct efx_channel *channel;
+	struct efx_tx_queue *tx_queue;
+
+	efx_for_each_channel(channel, efx) {
+		efx_for_each_channel_tx_queue(tx_queue, channel) {
+			efx_reado_table(efx, &txd_ptr_tbl,
+					FR_BZ_TX_DESC_PTR_TBL, tx_queue->queue);
+			if (EFX_OWORD_FIELD(txd_ptr_tbl,
+					    FRF_AZ_TX_DESCQ_FLUSH) ||
+			    EFX_OWORD_FIELD(txd_ptr_tbl,
+					    FRF_AZ_TX_DESCQ_EN)) {
+				netif_dbg(efx, hw, efx->net_dev,
+					  "flush did not complete on TXQ %d\n",
+					  tx_queue->queue);
+				i = false;
+			} else if (atomic_cmpxchg(&tx_queue->flush_outstanding,
+						  1, 0)) {
+				/* The flush is complete, but we didn't
+				 * receive a flush completion event
+				 */
+				netif_dbg(efx, hw, efx->net_dev,
+					  "flush complete on TXQ %d, so drain "
+					  "the queue\n", tx_queue->queue);
+				/* Don't need to increment drain_pending as it
+				 * has already been incremented for the queues
+				 * which did not drain
+				 */
+				efx_magic_event(channel,
+						EFX_CHANNEL_MAGIC_TX_DRAIN(
+							tx_queue));
+			}
+		}
+	}
+
+	return i;
+}
+
 /* Flush all the transmit queues, and continue flushing receive queues until
  * they're all flushed. Wait for the DRAIN events to be recieved so that there
  * are no more RX and TX events left on any channel. */
@@ -726,7 +772,8 @@ int efx_nic_flush_queues(struct efx_nic *efx)
 					     timeout);
 	}
 
-	if (atomic_read(&efx->drain_pending)) {
+	if (atomic_read(&efx->drain_pending) &&
+	    !efx_check_tx_flush_complete(efx)) {
 		netif_err(efx, hw, efx->net_dev, "failed to flush %d queues "
 			  "(rx %d+%d)\n", atomic_read(&efx->drain_pending),
 			  atomic_read(&efx->rxq_flush_outstanding),
@@ -1018,11 +1065,12 @@ efx_handle_tx_flush_done(struct efx_nic *efx, efx_qword_t *event)
 	if (qid < EFX_TXQ_TYPES * efx->n_tx_channels) {
 		tx_queue = efx_get_tx_queue(efx, qid / EFX_TXQ_TYPES,
 					    qid % EFX_TXQ_TYPES);
-
+		if (atomic_cmpxchg(&tx_queue->flush_outstanding, 1, 0)) {
 			efx_magic_event(tx_queue->channel,
 					EFX_CHANNEL_MAGIC_TX_DRAIN(tx_queue));
 		}
 	}
+}
 
 /* If this flush done event corresponds to a &struct efx_rx_queue: If the flush
  * was succesful then send an %EFX_CHANNEL_MAGIC_RX_DRAIN, otherwise add