Re: [PATCH v2 6/7] mailbox: bcm-flexrm-mailbox: Set msg_queue_len for each channel

[Anup Patel]

On Mon, Jul 24, 2017 at 10:06 PM, Jassi Brar <jassisinghbrar@xxxxxxxxx> wrote:
> On Mon, Jul 24, 2017 at 9:26 AM, Anup Patel <anup.patel@xxxxxxxxxxxx> wrote:
>> Hi Jassi,
>>
>> Sorry for the delayed response...
>>
>> On Fri, Jul 21, 2017 at 9:16 PM, Jassi Brar <jassisinghbrar@xxxxxxxxx> wrote:
>>> Hi Anup,
>>>
>>> On Fri, Jul 21, 2017 at 12:25 PM, Anup Patel <anup.patel@xxxxxxxxxxxx> wrote:
>>>> The Broadcom FlexRM ring (i.e. mailbox channel) can handle
>>>> larger number of messages queued in one FlexRM ring hence
>>>> this patch sets msg_queue_len for each mailbox channel to
>>>> be same as RING_MAX_REQ_COUNT.
>>>>
>>>> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxxxx>
>>>> Reviewed-by: Scott Branden <scott.branden@xxxxxxxxxxxx>
>>>> ---
>>>>  drivers/mailbox/bcm-flexrm-mailbox.c | 5 ++++-
>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/mailbox/bcm-flexrm-mailbox.c b/drivers/mailbox/bcm-flexrm-mailbox.c
>>>> index 9873818..20055a0 100644
>>>> --- a/drivers/mailbox/bcm-flexrm-mailbox.c
>>>> +++ b/drivers/mailbox/bcm-flexrm-mailbox.c
>>>> @@ -1683,8 +1683,11 @@ static int flexrm_mbox_probe(struct platform_device *pdev)
>>>>                 ret = -ENOMEM;
>>>>                 goto fail_free_debugfs_root;
>>>>         }
>>>> -       for (index = 0; index < mbox->num_rings; index++)
>>>> +       for (index = 0; index < mbox->num_rings; index++) {
>>>> +               mbox->controller.chans[index].msg_queue_len =
>>>> +                                               RING_MAX_REQ_COUNT;
>>>>                 mbox->controller.chans[index].con_priv = &mbox->rings[index];
>>>> +       }
>>>>
>>> While writing mailbox.c I wasn't unaware that there is the option to
>>> choose the queue length at runtime.
>>> The idea was to keep the code as simple as possible. I am open to
>>> making it a runtime thing, but first, please help me understand how
>>> that is useful here.
>>>
>>> I understand FlexRm has a ring buffer of RING_MAX_REQ_COUNT(1024)
>>> elements. Any message submitted to mailbox api can be immediately
>>> written onto the ringbuffer if there is some space.
>>> Is there any mechanism to report back to a client driver, if its
>>> message in ringbuffer failed "to be sent"?
>>> If there isn't any, then I think, in flexrm_last_tx_done() you should
>>> simply return true if there is some space left in the rung-buffer,
>>> false otherwise.
>>
>> Yes, we have error code in "struct brcm_message" to report back
>> errors from send_message. In our mailbox clients, we check
>> return value of mbox_send_message() and also the error code
>> in "struct brcm_message".
>>
> I meant after the message has been accepted in the ringbuffer but the
> remote failed to receive it.

Yes, even this case is handled.

In case of IO errors after message has been put in ring buffer, we get
completion message with error code and mailbox client drivers will
receive back "struct brcm_message" with error set.

You can refer flexrm_process_completions() for more details.

> There seems no such provision. IIANW, then you should be able to
> consider every message as "sent successfully" once it is in the ring
> buffer i.e, immediately after mbox_send_message() returns 0.
> In that case I would think you don't need more than a couple of
> entries out of MBOX_TX_QUEUE_LEN ?

What I am trying to suggest is that we can take upto 1024 messages
in a FlexRM ring but the MBOX_TX_QUEUE_LEN limits us queuing
more messages. This issue manifest easily when multiple CPUs
queues to same FlexRM ring (i.e. same mailbox channel).

Another quick fix is to make MBOX_TX_QUEUE_LEN as 1024 but
it will not be generic fix.

Regards,
Anup