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.

This commit works with the premise that the multi-threads' access to a
channel in blocking mode is serialized by clients, not by the mailbox
APIs, since the current mbox_send_message() in blocking mode does not
support multi-threads.

Signed-off-by: Joonwon Kang <joonwonkang@google.com>
Reviewed-by: Sudeep Holla <sudeep.holla@kernel.org>
---
v6: Remove the Cc tag from the commit message.
v5: Add note to the commit message that the current mailbox APIs in
    blocking mode do not support multi-threads.
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];
-- 
2.54.0.563.g4f69b47b94-goog

On Sun, May 10, 2026 at 12:41 AM Joonwon Kang <joonwonkang@google.com> wrote:
>
> 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.
>
> This commit works with the premise that the multi-threads' access to a
> channel in blocking mode is serialized by clients, not by the mailbox
> APIs, since the current mbox_send_message() in blocking mode does not
> support multi-threads.
>
> Signed-off-by: Joonwon Kang <joonwonkang@google.com>
> Reviewed-by: Sudeep Holla <sudeep.holla@kernel.org>
> ---
> v6: Remove the Cc tag from the commit message.
> v5: Add note to the commit message that the current mailbox APIs in
>     blocking mode do not support multi-threads.
> 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];
> --
> 2.54.0.563.g4f69b47b94-goog
>
Applied to mailbox/for-next
Thanks
Jassi