v4.19.13 snapshot.
diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h
new file mode 100644
index 0000000..4434871
--- /dev/null
+++ b/include/linux/mailbox_client.h
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2013-2014 Linaro Ltd.
+ * Author: Jassi Brar <jassisinghbrar@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __MAILBOX_CLIENT_H
+#define __MAILBOX_CLIENT_H
+
+#include <linux/of.h>
+#include <linux/device.h>
+
+struct mbox_chan;
+
+/**
+ * struct mbox_client - User of a mailbox
+ * @dev: The client device
+ * @tx_block: If the mbox_send_message should block until data is
+ * transmitted.
+ * @tx_tout: Max block period in ms before TX is assumed failure
+ * @knows_txdone: If the client could run the TX state machine. Usually
+ * if the client receives some ACK packet for transmission.
+ * Unused if the controller already has TX_Done/RTR IRQ.
+ * @rx_callback: Atomic callback to provide client the data received
+ * @tx_prepare: Atomic callback to ask client to prepare the payload
+ * before initiating the transmission if required.
+ * @tx_done: Atomic callback to tell client of data transmission
+ */
+struct mbox_client {
+ struct device *dev;
+ bool tx_block;
+ unsigned long tx_tout;
+ bool knows_txdone;
+
+ void (*rx_callback)(struct mbox_client *cl, void *mssg);
+ void (*tx_prepare)(struct mbox_client *cl, void *mssg);
+ void (*tx_done)(struct mbox_client *cl, void *mssg, int r);
+};
+
+struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,
+ const char *name);
+struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
+int mbox_send_message(struct mbox_chan *chan, void *mssg);
+void mbox_client_txdone(struct mbox_chan *chan, int r); /* atomic */
+bool mbox_client_peek_data(struct mbox_chan *chan); /* atomic */
+void mbox_free_channel(struct mbox_chan *chan); /* may sleep */
+
+#endif /* __MAILBOX_CLIENT_H */