Re: [PATCH v3 2/2] mailbox: Make mbox_send_message() return error code when tx fails

[Joonwon Kang <joonwonkang@google.com>]

> On Fri, Apr 3, 2026 at 10:19 AM Joonwon Kang <joonwonkang@google.com> wrote:
> >
> > > On Thu, Apr 2, 2026 at 12:07 PM 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(). 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.
> > > >
> > > Can you please share the scenario when this becomes necessary? This
> > > can potentially change the ground underneath some clients, so we have
> > > to be sure this is really useful.
> >
> > I would say the problem here is generic enough to apply to all the cases where
> > the send result needs to be checked. Since the return value of the send API is
> > not the real send result, any users who believe that this blocking send API
> > will return the real send result could fall for that. For example, users may
> > think the send was successful even though it was not actually. I believe it is
> > uncommon that users have to register a callback solely to get the send result
> > even though they are using the blocking send API already. Also, I guess there
> > is no special reason why only the mailbox send API should work this way among
> > other typical blocking send APIs. For these reasons, this patch makes the send
> > API return the real send result. This way, users will not need to register the
> > redundant callback and I think the return value will align with their common
> > expectation.
> >
> Clients submit a message into the Mailbox subsystem to be sent out to
> the remote side which can happen immediately or later.
> If submission fails, clients get immediately notified. If transmission
> fails (which is now internal to the subsystem) it is reported to the
> client by a callback.
> If the API was called mbox_submit_message (which it actually is)
> instead of mbox_send_message, there would be no confusion.
> We can argue how good/bad the current implementation is, but the fact
> is that it is here. And I am reluctant to cause churn without good
> reason.
> Again, as I said, any, _legal_, setup scenario will help me come over
> my reluctance.
> 
> Thanks
> Jassi

Hi Jassi, can we continue discussing this issue from where we left off last
time?

Thanks,
Joonwon Kang