linux-kernel - Re: [PATCH] mailbox: check mailbox queue is full or not

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Message-ID: <20250926073735.GD8204@nxa18884-linux.ap.freescale.net>
Date: Fri, 26 Sep 2025 15:37:35 +0800
From: Peng Fan <peng.fan@....nxp.com>
To: Tanmay Shah <tanmay.shah@....com>
Cc: jassisinghbrar@...il.com, andersson@...nel.org,
	mathieu.poirier@...aro.org, linux-kernel@...r.kernel.org,
	linux-remoteproc@...r.kernel.org
Subject: Re: [PATCH] mailbox: check mailbox queue is full or not

Hi Tanmay,

On Thu, Sep 25, 2025 at 11:50:44AM -0700, Tanmay Shah 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. This API can help avoid false positive warning from mailbox
>framework "Try increasing MBOX_TX_QUEUE_LEN".
>
>Signed-off-by: Tanmay Shah <tanmay.shah@....com>
>---
> drivers/mailbox/mailbox.c               | 24 ++++++++++++++++++++++++
> drivers/remoteproc/xlnx_r5_remoteproc.c |  4 ++++
> include/linux/mailbox_client.h          |  1 +

The mailbox and remoteproc should be separated.

> 3 files changed, 29 insertions(+)
>
>diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
>index 5cd8ae222073..7afdb2c9006d 100644
>--- a/drivers/mailbox/mailbox.c
>+++ b/drivers/mailbox/mailbox.c
>@@ -217,6 +217,30 @@ bool mbox_client_peek_data(struct mbox_chan *chan)
> }
> EXPORT_SYMBOL_GPL(mbox_client_peek_data);
> 
>+/**
>+ * mbox_queue_full - check if mailbox queue is full or not
>+ * @chan: Mailbox channel assigned to this client.
>+ *
>+ * Clients can choose not to send new msg if mbox queue is full.
>+ *
>+ * Return: true if queue is full else false. < 0 for error
>+ */
>+int mbox_queue_full(struct mbox_chan *chan)
>+{
>+	unsigned long flags;
>+	int res;
>+
>+	if (!chan)
>+		return -EINVAL;
>+
>+	spin_lock_irqsave(&chan->lock, flags);

Use scoped_guard.

>+	res = (chan->msg_count == (MBOX_TX_QUEUE_LEN - 1));
>+	spin_unlock_irqrestore(&chan->lock, flags);
>+
>+	return res;
>+}
>+EXPORT_SYMBOL_GPL(mbox_queue_full);

add_to_rbuf is able to return ENOBUFS when call mbox_send_message.
Does checking mbox_send_message return value works for you?

>+
> /**
>  * mbox_send_message -	For client to submit a message to be
>  *				sent to the remote.

Regards
Peng