sfc: rewrite efx_tx_may_pio

Use efx_for_each_channel_tx_queue() rather than efx_tx_queue_partner().
Make some related simplifications of efx_nic_tx_is_empty() to remove
 entry points that aren't used.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 25 insertions, 1 deletions

diff --git a/drivers/net/ethernet/sfc/tx.c b/drivers/net/ethernet/sfc/tx.c
index b868920b680c..48d91b26f1a2 100644
--- a/drivers/net/ethernet/sfc/tx.c
+++ b/drivers/net/ethernet/sfc/tx.c
@@ -264,6 +264,30 @@ static int efx_enqueue_skb_pio(struct efx_tx_queue *tx_queue,
 	++tx_queue->insert_count;
 	return 0;
 }
+
+/* Decide whether we can use TX PIO, ie. write packet data directly into
+ * a buffer on the device.  This can reduce latency at the expense of
+ * throughput, so we only do this if both hardware and software TX rings
+ * are empty, including all queues for the channel.  This also ensures that
+ * only one packet at a time can be using the PIO buffer. If the xmit_more
+ * flag is set then we don't use this - there'll be another packet along
+ * shortly and we want to hold off the doorbell.
+ */
+static bool efx_tx_may_pio(struct efx_tx_queue *tx_queue)
+{
+	struct efx_channel *channel = tx_queue->channel;
+
+	if (!tx_queue->piobuf)
+		return false;
+
+	EFX_WARN_ON_ONCE_PARANOID(!channel->efx->type->option_descriptors);
+
+	efx_for_each_channel_tx_queue(tx_queue, channel)
+		if (!efx_nic_tx_is_empty(tx_queue, tx_queue->packet_write_count))
+			return false;
+
+	return true;
+}
 #endif /* EFX_USE_PIO */
 
 /* Send any pending traffic for a channel. xmit_more is shared across all
@@ -326,7 +350,7 @@ netdev_tx_t __efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb
 			goto err;
 #ifdef EFX_USE_PIO
 	} else if (skb_len <= efx_piobuf_size && !xmit_more &&
-		   efx_nic_may_tx_pio(tx_queue)) {
+		   efx_tx_may_pio(tx_queue)) {
 		/* Use PIO for short packets with an empty queue. */
 		if (efx_enqueue_skb_pio(tx_queue, skb))
 			goto err;