Message-ID: <CABb+yY3fwPTSc0PKh44uvgdbvQJhu-X3O_L5EtumB6ovsaOdSw@mail.gmail.com>
Date:   Thu, 27 Jul 2017 10:29:04 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Anup Patel <anup.patel@...adcom.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Scott Branden <sbranden@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH v2 6/7] mailbox: bcm-flexrm-mailbox: Set msg_queue_len for
 each channel

On Thu, Jul 27, 2017 at 9:25 AM, Anup Patel <anup.patel@...adcom.com> wrote:
> On Tue, Jul 25, 2017 at 9:37 PM, Jassi Brar <jassisinghbrar@...il.com> wrote:
>> On Tue, Jul 25, 2017 at 11:11 AM, Anup Patel <anup.patel@...adcom.com> wrote:
>>> On Mon, Jul 24, 2017 at 10:06 PM, Jassi Brar <jassisinghbrar@...il.com> wrote:
>>>> On Mon, Jul 24, 2017 at 9:26 AM, Anup Patel <anup.patel@...adcom.com> wrote:
>>>>> Hi Jassi,
>>>>>
>>>>> Sorry for the delayed response...
>>>>>
>>>>> On Fri, Jul 21, 2017 at 9:16 PM, Jassi Brar <jassisinghbrar@...il.com> wrote:
>>>>>> Hi Anup,
>>>>>>
>>>>>> On Fri, Jul 21, 2017 at 12:25 PM, Anup Patel <anup.patel@...adcom.com> 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@...adcom.com>
>>>>>>> Reviewed-by: Scott Branden <scott.branden@...adcom.com>
>>>>>>> ---
>>>>>>>  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.
>>>
It doesn't seem to be what I suggest. I see two issues in
flexrm_process_completions()
1) It calls mbox_send_message(), which is a big NO for a controller
driver. Why should you have one more message stored outside of
ringbuffer?

2) It calls mbox_chan_received_data()  which is for messages received
from the remote. And not the way to report failed _transmission_, for
which the api calls back mbox_client.tx_done() .  In your client
driver please populate mbox_client.tx_done() and see which message is
reported "sent fine" when.


>>>> 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).
>>>
>> OK then, I guess we have to make the queue length a runtime decision.
>
> Do you agree with approach taken by PATCH5 and PATCH6 to
> make queue length runtime?
>
I agree that we may have to get the queue length from platform, if
MBOX_TX_QUEUE_LEN is limiting performance. That will be easier on both
of us. However I suspect the right fix for _this_ situation is in
flexrm driver. See above.

>>
>> BTW, is it a practical use case that needs to queue upto 1024
>> requests? Or are you just testing?
>
> Yes, we just need bigger queue length for FlexRM but we
> choose 1024 (max limit) to avoid changing it again in future.
>
How does the client use the api? Does it work in blocking mode i.e, is
tx_block set ? Is it available somewhere I can have a look?

Thanks.

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