[PATCH] mailbox: Clarify multi-thread is not supported in blocking mode

[PATCH] mailbox: Clarify multi-thread is not supported in blocking mode

[Joonwon Kang]

Unlike in non-blocking mode, multi-thread has not been supported in
blocking mode. This commit is to prevent clients from having wrong
assumption by explicitly specifying this fact to the API doc.

Cc: stable@vger.kernel.org
Signed-off-by: Joonwon Kang <joonwonkang@google.com>
---
v1: Abandon the previous attempts to support multi-thread in blocking
  mode and instead declare it is not supported.

 drivers/mailbox/mailbox.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index bbc9fd75a95f..b00f7a32e866 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -258,6 +258,10 @@ EXPORT_SYMBOL_GPL(mbox_chan_tx_slots_available);
  * over the chan, i.e, tx_done() is made.
  * This function could be called from atomic context as it simply
  * queues the data and returns a token against the request.
+ *  In blocking mode, it is caller's responsibility to serialize threads'
+ * access to a channel if multi-threads are to send messages through the
+ * same channel, i.e. caller should not call this function until any
+ * previous call returns.
  *
  * Return: Non-negative integer for successful submission (non-blocking mode)
  *	or transmission over chan (blocking mode).
-- 
2.54.0.rc1.555.g9c883467ad-goog

[PATCH v4] mailbox: Make mbox_send_message() return error code when tx fails

[Joonwon Kang]

When the mailbox controller failed transmitting message, the error code
was only passed to the client's tx done handler and not to
mbox_send_message() in blocking mode. For this reason, the function could
return a false success. This commit resolves the issue by introducing the
tx status and checking it before mbox_send_message() returns.

Cc: stable@vger.kernel.org
Signed-off-by: Joonwon Kang <joonwonkang@google.com>
---
v4: Detach it from the previous commit that supports multi-thread in
  blocking mode and rebase it on the latest for-next branch.
v3: No major patch since v1.

 drivers/mailbox/mailbox.c          | 6 +++++-
 include/linux/mailbox_controller.h | 2 ++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index b00f7a32e866..066702e5a46f 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -98,8 +98,10 @@ static void tx_tick(struct mbox_chan *chan, int r)
 	if (chan->cl->tx_done)
 		chan->cl->tx_done(chan->cl, mssg, r);
 
-	if (r != -ETIME && chan->cl->tx_block)
+	if (r != -ETIME && chan->cl->tx_block) {
+		chan->tx_status = r;
 		complete(&chan->tx_complete);
+	}
 }
 
 static enum hrtimer_restart txdone_hrtimer(struct hrtimer *hrtimer)
@@ -295,6 +297,8 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg)
 		if (ret == 0) {
 			t = -ETIME;
 			tx_tick(chan, t);
+		} else if (chan->tx_status < 0) {
+			t = chan->tx_status;
 		}
 	}
 
diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
index dc93287a2a01..26a238a6f941 100644
--- a/include/linux/mailbox_controller.h
+++ b/include/linux/mailbox_controller.h
@@ -120,6 +120,7 @@ struct mbox_controller {
  * @txdone_method:	Way to detect TXDone chosen by the API
  * @cl:			Pointer to the current owner of this channel
  * @tx_complete:	Transmission completion
+ * @tx_status:		Transmission status
  * @active_req:		Currently active request hook
  * @msg_count:		No. of mssg currently queued
  * @msg_free:		Index of next available mssg slot
@@ -132,6 +133,7 @@ struct mbox_chan {
 	unsigned txdone_method;
 	struct mbox_client *cl;
 	struct completion tx_complete;
+	int tx_status;
 	void *active_req;
 	unsigned msg_count, msg_free;
 	void *msg_data[MBOX_TX_QUEUE_LEN];
-- 
2.54.0.rc1.555.g9c883467ad-goog