diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h
index 307d9ca..1726ccb 100644
--- a/include/linux/mailbox_client.h
+++ b/include/linux/mailbox_client.h
@@ -25,6 +25,8 @@
  *			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 {
@@ -34,6 +36,7 @@
 	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);
 };