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

[Tanmay Shah <tanmay.shah@amd.com>]

On 10/7/25 2:58 PM, Jassi Brar wrote:
> On Tue, Oct 7, 2025 at 10:19 AM Tanmay Shah <tanmay.shah@amd.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@amd.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.
> 

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