3 files changed, 33 insertions, 0 deletions

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index 08ce9a1ab53a..6abb35ff49fa 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -284,6 +284,34 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg)
 EXPORT_SYMBOL_GPL(mbox_send_message);
 
 /**
+ * mbox_flush - flush a mailbox channel
+ * @chan: mailbox channel to flush
+ * @timeout: time, in milliseconds, to allow the flush operation to succeed
+ *
+ * Mailbox controllers that need to work in atomic context can implement the
+ * ->flush() callback to busy loop until a transmission has been completed.
+ * The implementation must call mbox_chan_txdone() upon success. Clients can
+ * call the mbox_flush() function at any time after mbox_send_message() to
+ * flush the transmission. After the function returns success, the mailbox
+ * transmission is guaranteed to have completed.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+int mbox_flush(struct mbox_chan *chan, unsigned long timeout)
+{
+        int ret;
+
+        if (!chan->mbox->ops->flush)
+                return -ENOTSUPP;
+
+        ret = chan->mbox->ops->flush(chan, timeout);
+        if (ret < 0)
+                tx_tick(chan, ret);
+
+        return ret;
+}
+
+/**
  * mbox_request_channel - Request a mailbox channel.
  * @cl: Identity of the client requesting the channel.
  * @index: Index of mailbox specifier in 'mboxes' property.
diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h
index 44348710953f..faa7da3c9c8b 100644
--- a/include/linux/mailbox_client.h
+++ b/include/linux/mailbox_client.h
@@ -44,6 +44,7 @@ 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);
+int mbox_flush(struct mbox_chan *chan, unsigned long timeout);
 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 */
diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
index 9b0b21207345..4994a438444c 100644
--- a/include/linux/mailbox_controller.h
+++ b/include/linux/mailbox_controller.h
@@ -24,6 +24,9 @@ struct mbox_chan;
  *              transmission of data is reported by the controller via
  *              mbox_chan_txdone (if it has some TX ACK irq). It must not
  *              sleep.
+ * @flush:      Called when a client requests transmissions to be blocking but
+ *              the context doesn't allow sleeping. Typically the controller
+ *              will implement a busy loop waiting for the data to flush out.
  * @startup:    Called when a client requests the chan. The controller
  *              could ask clients for additional parameters of communication
  *              to be provided via client's chan_data. This call may
@@ -46,6 +49,7 @@ struct mbox_chan;
  */
 struct mbox_chan_ops {
         int (*send_data)(struct mbox_chan *chan, void *data);
+        int (*flush)(struct mbox_chan *chan, unsigned long timeout);
         int (*startup)(struct mbox_chan *chan);
         void (*shutdown)(struct mbox_chan *chan);
         bool (*last_tx_done)(struct mbox_chan *chan);