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

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Message-ID: <CABb+yY1Y90S_dbybMT07PTvmy60W2mt3mHdP56sp6DO75bpuNw@mail.gmail.com>
Date: Sat, 15 Nov 2025 11:38:47 -0600
From: Jassi Brar <jassisinghbrar@...il.com>
To: tanmay.shah@....com
Cc: andersson@...nel.org, mathieu.poirier@...aro.org, 
	linux-kernel@...r.kernel.org, linux-remoteproc@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mailbox: check mailbox queue is full or not

On Wed, Oct 15, 2025 at 10:27 AM Tanmay Shah <tanmay.shah@....com> wrote:
> >>> 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 ?
> >
>
> Hi Jassi,
>
> I looked into this further. Looks like it's not possible to introduce
> msg_slot_ro in the client data structure as of today. Because multiple
> drivers are sharing same client for "tx" and "rx" both channels.
> [references: 1, 2, 3]
>
> so, msg_slot_ro won't be calculated correctly I believe.
>
I don't see it. Can you please explain how the calculated value could be wrong?

thnx
-jassi