net: ipa: expand last transaction check

Transactions to send data for a network device can be allocated at
any time up until the point the TX queue is stopped.  It is possible
for ipa_start_xmit() to be called in one context just before a
the transmit queue is stopped in another.

Update gsi_channel_trans_last() so that for TX channels the
allocated and pending transaction lists are checked--in addition
to the completed and polled lists--to determine the "last"
transaction.  This means any transaction that has been allocated
before the TX queue is stopped will be allowed to complete before
we conclude the channel is quiesced.

Rework the function a bit to use a list pointer and gotos.
Signed-off-by: Alex Elder <elder@linaro.org>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ipa/gsi.c

@@ -725,22 +725,38 @@ static void gsi_evt_ring_program(struct gsi *gsi, u32 evt_ring_id)
 	gsi_evt_ring_doorbell(gsi, evt_ring_id, 0);
 }
 
-/* Return the last (most recent) transaction completed on a channel. */
+/* Find the transaction whose completion indicates a channel is quiesced */
 static struct gsi_trans *gsi_channel_trans_last(struct gsi_channel *channel)
 {
 	struct gsi_trans_info *trans_info = &channel->trans_info;
+	const struct list_head *list;
 	struct gsi_trans *trans;
 
 	spin_lock_bh(&trans_info->spinlock);
 
-	if (!list_empty(&trans_info->complete))
-		trans = list_last_entry(&trans_info->complete,
-					struct gsi_trans, links);
-	else if (!list_empty(&trans_info->polled))
-		trans = list_last_entry(&trans_info->polled,
-					struct gsi_trans, links);
-	else
-		trans = NULL;
+	/* There is a small chance a TX transaction got allocated just
+	 * before we disabled transmits, so check for that.
+	 */
+	if (channel->toward_ipa) {
+		list = &trans_info->alloc;
+		if (!list_empty(list))
+			goto done;
+		list = &trans_info->pending;
+		if (!list_empty(list))
+			goto done;
+	}
+
+	/* Otherwise (TX or RX) we want to wait for anything that
+	 * has completed, or has been polled but not released yet.
+	 */
+	list = &trans_info->complete;
+	if (!list_empty(list))
+		goto done;
+	list = &trans_info->polled;
+	if (list_empty(list))
+		list = NULL;
+done:
+	trans = list ? list_last_entry(list, struct gsi_trans, links) : NULL;
 
 	/* Caller will wait for this, so take a reference */
 	if (trans)