[PATCH v2 01/15] mailbox: Deprecate NULL mbox messages; Introduce mbox_ring_doorbell()

[Jassi Brar]

Hi Douglas,

On Sat, Feb 7, 2026 at 10:04 PM Douglas Anderson <dianders at chromium.org> wrote:
> @@ -249,6 +255,28 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg)
>         if (!chan || !chan->cl)
>                 return -EINVAL;
>
> +       /*
> +        * The mailbox core gets confused when mbox_send_message() is called
> +        * with NULL messages since the code directly stores messages in
> +        * `active_req` and assumes that a NULL `active_req` means no request
> +        * is active. This causes the core to call the mailbox controller a
> +        * second time even if the previous message hasn't finished and also
> +        * means the client's tx_done() callback will never be called. However,
> +        * clients historically passed NULL anyway. Deprecate passing NULL
> +        * here by adding a warning.
> +        *
> +        * Clients who don't have a message should switch to using
> +        * mbox_ring_doorbell(), which explicitly documents the immediate
> +        * sending of doorbells, the lack of txdone, and what happens if you
> +        * mix doorbells and normal messages.
> +        *
> +        * TODO: when it's certain that all clients have transitioned, consider
> +        * changing this to return -EINVAL.
> +        */
> +       if (!mssg)
> +               dev_warn_once(chan->mbox->dev,
> +                             "NULL mailbox messages are deprecated\n");
>
Nit: maybe  "NULL mailbox messages are deprecated, use
mbox_ring_doorbell instead" ?

Thanks,
Jassi