mailbox: Support blocking transfers in atomic context

The mailbox framework supports blocking transfers via completions for
clients that can sleep. In order to support blocking transfers in cases
where the transmission is not permitted to sleep, add a new ->flush()
callback that controller drivers can implement to busy loop until the
transmission has been completed. A new mbox_flush() function can be
called by mailbox consumers in atomic context to make sure a transfer
has completed.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

1 files changed, 28 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.