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

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Message-ID: <a5b03f04-9add-4adc-abe8-95024d05b9b9@amd.com>
Date: Wed, 8 Oct 2025 10:55:56 -0500
From: Tanmay Shah <tanmay.shah@....com>
To: Jassi Brar <jassisinghbrar@...il.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 10/7/25 2:58 PM, Jassi Brar wrote:
> 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.
> 

Sure, that makes sense. Will change in v3.

> thanks
> jassi