greybus: connection: add helper to disable incoming operations

Add helper to disable and flush incoming operations.

This is intended to be used by core to flush any incoming requests
before calling driver disconnect, but could potentially later be
exported for driver use as well.

Note that we currently flush all incoming operation and allow the
request handlers to run, but cancel any responses sent. This may need to
be refined later.
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/connection.c

@@ -386,6 +386,42 @@ static void gb_connection_cancel_operations(struct gb_connection *connection,
 	}
 }
 
+/*
+ * Cancel all active incoming operations on a connection.
+ *
+ * Locking: Called with connection lock held and state set to ENABLED_TX.
+ */
+static void
+gb_connection_flush_incoming_operations(struct gb_connection *connection,
+						int errno)
+{
+	struct gb_operation *operation;
+	bool incoming;
+
+	while (!list_empty(&connection->operations)) {
+		incoming = false;
+		list_for_each_entry(operation, &connection->operations,
+								links) {
+			if (gb_operation_is_incoming(operation)) {
+				gb_operation_get(operation);
+				incoming = true;
+				break;
+			}
+		}
+
+		if (!incoming)
+			break;
+
+		spin_unlock_irq(&connection->lock);
+
+		/* FIXME: flush, not cancel? */
+		gb_operation_cancel_incoming(operation, errno);
+		gb_operation_put(operation);
+
+		spin_lock_irq(&connection->lock);
+	}
+}
+
 int gb_connection_enable(struct gb_connection *connection,
 				gb_request_handler_t handler)
 {
@@ -450,6 +486,24 @@ int gb_connection_enable(struct gb_connection *connection,
 }
 EXPORT_SYMBOL_GPL(gb_connection_enable);
 
+void gb_connection_disable_rx(struct gb_connection *connection)
+{
+	mutex_lock(&connection->mutex);
+
+	spin_lock_irq(&connection->lock);
+	if (connection->state != GB_CONNECTION_STATE_ENABLED) {
+		spin_unlock_irq(&connection->lock);
+		goto out_unlock;
+	}
+	connection->state = GB_CONNECTION_STATE_ENABLED_TX;
+	gb_connection_flush_incoming_operations(connection, -ESHUTDOWN);
+	connection->handler = NULL;
+	spin_unlock_irq(&connection->lock);
+
+out_unlock:
+	mutex_unlock(&connection->mutex);
+}
+
 void gb_connection_disable(struct gb_connection *connection)
 {
 	mutex_lock(&connection->mutex);

drivers/staging/greybus/connection.h

@@ -75,6 +75,7 @@ static inline int gb_connection_enable_tx(struct gb_connection *connection)
 {
 	return gb_connection_enable(connection, NULL);
 }
+void gb_connection_disable_rx(struct gb_connection *connection);
 void gb_connection_disable(struct gb_connection *connection);
 
 int gb_connection_legacy_init(struct gb_connection *connection);