Re: [PATCH v2 1/2] mailbox: check mailbox queue is full or not

[Tanmay Shah]

On 10/7/25 2:58 PM, Jassi Brar wrote:
> On Tue, Oct 7, 2025 at 10:19 AM Tanmay Shah <tanmay.shah@xxxxxxx> 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  can help avoid false positive warning from mailbox
> > framework "Try increasing MBOX_TX_QUEUE_LEN".
> >
> > Signed-off-by: Tanmay Shah <tanmay.shah@xxxxxxx>
> > ---
> >
> > v2:
> >    - Separate patch for remoteproc subsystem.
> >    - Change design and introduce msg_slot_ro field for each channel
> >      instead of API. Clients can use this variable directly.
> >    - Remove mbox_queue_full API
> >
> >   drivers/mailbox/mailbox.c          | 3 +++
> >   include/linux/mailbox_controller.h | 2 ++
> >   2 files changed, 5 insertions(+)
> >
> > diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> > index 5cd8ae222073..c2e187aa5d22 100644
> > --- a/drivers/mailbox/mailbox.c
> > +++ b/drivers/mailbox/mailbox.c
> > @@ -35,6 +35,7 @@ static int add_to_rbuf(struct mbox_chan *chan, void *mssg)
> >          idx = chan->msg_free;
> >          chan->msg_data[idx] = mssg;
> >          chan->msg_count++;
> > +       chan->msg_slot_ro = (MBOX_TX_QUEUE_LEN - chan->msg_count);
> >
> >          if (idx == MBOX_TX_QUEUE_LEN - 1)
> >                  chan->msg_free = 0;
> > @@ -70,6 +71,7 @@ static void msg_submit(struct mbox_chan *chan)
> >                  if (!err) {
> >                          chan->active_req = data;
> >                          chan->msg_count--;
> > +                       chan->msg_slot_ro = (MBOX_TX_QUEUE_LEN - chan->msg_count);
> No, I had suggested adding this info in client structure.
> There is no point in carrying msg_count and msg_slot_ro in mbox_chan.
> The client needs this info but can/should not access the chan internals.

Hi Jassi,

If I move msg_slot_ro to mbox_client that means, each channel needs its 
own client structure. But it is possible to map single client to 
multiple channels.

How about if I rename msg_slot_ro to msg_slot_tx_ro -> that says this 
field should be used only for "tx" channel.

Or is it must to map unique client data structure to each channel? If 
so, can I update mbox_client structure documentation ?

Thanks,
Tanmay.

> thanks
> jassi