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

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Message-ID: <CABb+yY0m_Whm1F7d2ub+vhn0eTb47UC9g=JvpLnWh-2E1oo52A@mail.gmail.com>
Date: Tue, 7 Oct 2025 14:58:32 -0500
From: Jassi Brar <jassisinghbrar@...il.com>
To: Tanmay Shah <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 Tue, Oct 7, 2025 at 10:19 AM Tanmay Shah <tanmay.shah@....com> 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@....com>
> ---
>
> 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.

thanks
jassi