On Wed, Dec 17, 2025 at 3:27 PM Tanmay Shah <[email protected]> wrote:
>
> Sometimes clients need to know if mailbox queue is full or not before
> posting new message via mailbox. If mailbox queue is full clients can
> choose not to post new message. This doesn't mean current queue length
> should be increased, but clients may want to wait till previous Tx is
> done. Introduce variable per channel to track available msg slots.
> Clients can check this variable and decide not to send new message if
> it is 0. This will help avoid false positive warning from mailbox
> framework "Try increasing MBOX_TX_QUEUE_LEN".
>
> Signed-off-by: Tanmay Shah <[email protected]>
> ---
> drivers/mailbox/mailbox.c | 3 +++
> include/linux/mailbox_client.h | 2 ++
> 2 files changed, 5 insertions(+)
>
> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> index 2acc6ec229a4..b7ae5c173143 100644
> --- a/drivers/mailbox/mailbox.c
> +++ b/drivers/mailbox/mailbox.c
> @@ -36,6 +36,7 @@ static int add_to_rbuf(struct mbox_chan *chan, void *mssg)
> idx = chan->msg_free;
> chan->msg_data[idx] = mssg;
> chan->msg_count++;
> + chan->cl->msg_slot_ro = (MBOX_TX_QUEUE_LEN - chan->msg_count);
>
msg_count is protected by a lock and limited within MBOX_TX_QUEUE_LEN,
so how about simply chan->cl->msg_slot_ro--;
> if (idx == MBOX_TX_QUEUE_LEN - 1)
> chan->msg_free = 0;
> @@ -71,6 +72,7 @@ static void msg_submit(struct mbox_chan *chan)
> if (!err) {
> chan->active_req = data;
> chan->msg_count--;
> + chan->cl->msg_slot_ro = (MBOX_TX_QUEUE_LEN -
> chan->msg_count);
>
Similarly chan->cl->msg_slot_ro++ ?
> }
> }
>
> @@ -321,6 +323,7 @@ static int __mbox_bind_client(struct mbox_chan *chan,
> struct mbox_client *cl)
> chan->msg_count = 0;
> chan->active_req = NULL;
> chan->cl = cl;
> + chan->cl->msg_slot_ro = MBOX_TX_QUEUE_LEN;
> init_completion(&chan->tx_complete);
>
> if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
> diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h
> index c6eea9afb943..a073fb0c03d1 100644
> --- a/include/linux/mailbox_client.h
> +++ b/include/linux/mailbox_client.h
> @@ -17,6 +17,7 @@ struct mbox_chan;
> * @dev: The client device
> * @tx_block: If the mbox_send_message should block until data is
> * transmitted.
> + * @msg_slot_ro: msg slots remaining for this client's channel.
> * @tx_tout: Max block period in ms before TX is assumed failure
> * @knows_txdone: If the client could run the TX state machine. Usually
> * if the client receives some ACK packet for
> transmission.
> @@ -29,6 +30,7 @@ struct mbox_chan;
> struct mbox_client {
> struct device *dev;
> bool tx_block;
> + unsigned int msg_slot_ro;
>
maybe call it 'tx_slots_available_ro' ?
Thanks
