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-rw-r--r--include/linux/mailbox_controller.h3
1 files changed, 3 insertions, 0 deletions
diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
index 16fef421c30c..e3896b08f22e 100644
--- a/include/linux/mailbox_controller.h
+++ b/include/linux/mailbox_controller.h
@@ -12,6 +12,9 @@
struct mbox_chan;
+/* Sentinel value distinguishing "no active request" from "NULL message data" */
+#define MBOX_NO_MSG ((void *)-1)
+
#define TXDONE_BY_IRQ BIT(0) /* controller has remote RTR irq */
#define TXDONE_BY_POLL BIT(1) /* controller can read status of last TX */
#define TXDONE_BY_ACK BIT(2) /* S/W ACK received by Client ticks the TX */