[PATCH 7/7] mailbox: goog-mba: Introduce the goog-mba mailbox driver

[Jassi Brar]

Hi Douglas,

On Tue, Jul 14, 2026 at 5:24 PM Douglas Anderson <dianders at chromium.org> wrote:
....
> +
> +/**
> + * goog_mba_handle_tx_interrupt() - Handle interrupt that remote Acked our msg.
> + * @goog_mbox: The mailbox info.
> + */
> +static void goog_mba_handle_tx_interrupt(struct goog_mbox_info *goog_mbox)
> +{
> +       unsigned int reqs_completed;
> +       int i;
> +
> +       /*
> +        * ACK interrupt needs to be cleared before reading CLIENT_OUTSTANDING_MSG.
> +        * Then if a "race" happens and another message gets Acked after we clear
> +        * but before we read CLIENT_OUTSTANDING_MSG then the worst that will
> +        * happen is we'll get a followup interrupt that will show 0 reqs_completed.
> +        */
> +       writel(CLIENT_IRQ_STATUS_ACK_INT, goog_mbox->iomem + CLIENT_IRQ_STATUS_OFFSET);
> +
> +       if (goog_mbox->queue_mode) {
> +               u32 outstanding_msgs;
> +
> +               outstanding_msgs = readl(goog_mbox->iomem + CLIENT_OUTSTANDING_MSG);
> +               spin_lock(&goog_mbox->lock);
> +
> +               if (goog_mbox->outstanding_msgs >= outstanding_msgs) {
> +                       reqs_completed = goog_mbox->outstanding_msgs - outstanding_msgs;
> +               } else {
> +                       /*
> +                        * The hardware's track of outstanding messages should always
> +                        * be less than or equal to the number of messages we queued.
> +                        * If it thinks there are more messages outstanding than we
> +                        * queued, something is wrong. Assume nothing was completed.
> +                        */
> +                       dev_warn_ratelimited(goog_mbox->mba->dev,
> +                                            "%pOFP: unexpected outstanding msgs: %u -> %u\n",
> +                                            goog_mbox->np, goog_mbox->outstanding_msgs,
> +                                            outstanding_msgs);
> +                       reqs_completed = 0;
> +               }
> +               goog_mbox->outstanding_msgs = outstanding_msgs;
> +               spin_unlock(&goog_mbox->lock);
> +
> +               trace_goog_mba_process_q_txdone(goog_mbox, reqs_completed, outstanding_msgs);
> +       } else {
> +               reqs_completed = 1;
> +               trace_goog_mba_process_nq_txdone(goog_mbox);
> +       }
> +
> +       for (i = 0; i < reqs_completed; i++)
> +               mbox_chan_txdone(&goog_mbox->chan, 0);

The patchset doesn't say much about the clients but if the platform
works like this, I have a strong feeling we can do without introducing
mbox_controller.has_queue.
Just use the msg_data[] ringbuffer -- we can avoid changing the core
internals and you will still get ACK for each message.
What are the clients going to be like?

Regards,
Jassi