From: Jassi Brar <[email protected]> Clients sometimes need to know whether the mailbox TX queue has room before posting a new message. Rather than exposing internal queue state through a struct field, provide a proper accessor function that returns the number of available slots for a given channel.
This lets clients choose to back off when the queue is full instead of hitting the -ENOBUFS error path and the misleading "Try increasing MBOX_TX_QUEUE_LEN" warning. Signed-off-by: Jassi Brar <[email protected]> --- drivers/mailbox/mailbox.c | 23 +++++++++++++++++++++++ include/linux/mailbox_client.h | 1 + 2 files changed, 24 insertions(+) diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c index 2acc6ec229a4..22eb8f3213be 100644 --- a/drivers/mailbox/mailbox.c +++ b/drivers/mailbox/mailbox.c @@ -218,6 +218,29 @@ bool mbox_client_peek_data(struct mbox_chan *chan) } EXPORT_SYMBOL_GPL(mbox_client_peek_data); +/** + * mbox_chan_tx_slots_available - Query the number of available TX queue slots. + * @chan: Mailbox channel to query. + * + * Clients may call this to check how many messages can be queued via + * mbox_send_message() before the channel's TX queue is full. This helps + * clients avoid the -ENOBUFS error without needing to increase + * MBOX_TX_QUEUE_LEN. + * This can be called from atomic context. + * + * Return: Number of available slots in the channel's TX queue. + */ +unsigned int mbox_chan_tx_slots_available(struct mbox_chan *chan) +{ + unsigned int ret; + + guard(spinlock_irqsave)(&chan->lock); + ret = MBOX_TX_QUEUE_LEN - chan->msg_count; + + return ret; +} +EXPORT_SYMBOL_GPL(mbox_chan_tx_slots_available); + /** * mbox_send_message - For client to submit a message to be * sent to the remote. diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h index c6eea9afb943..e5997120f45c 100644 --- a/include/linux/mailbox_client.h +++ b/include/linux/mailbox_client.h @@ -45,6 +45,7 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg); int mbox_flush(struct mbox_chan *chan, unsigned long timeout); void mbox_client_txdone(struct mbox_chan *chan, int r); /* atomic */ bool mbox_client_peek_data(struct mbox_chan *chan); /* atomic */ +unsigned int mbox_chan_tx_slots_available(struct mbox_chan *chan); /* atomic */ void mbox_free_channel(struct mbox_chan *chan); /* may sleep */ #endif /* __MAILBOX_CLIENT_H */ -- 2.43.0
