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

On Thu, Jul 27, 2017 at 11:20 AM, Anup Patel [off-list ref] wrote:

On Thu, Jul 27, 2017 at 10:29 AM, Jassi Brar [off-list ref] wrote:

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Sorry for the delayed response...

On Fri, Jul 21, 2017 at 9:16 PM, Jassi Brar [off-list ref] wrote:

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Hi Anup,

On Fri, Jul 21, 2017 at 12:25 PM, Anup Patel [off-list ref] wrote:

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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 <redacted>
Reviewed-by: Scott Branden <scott.branden@broadcom.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?

The "last_pending_msg" in each FlexRM ring was added to fit FlexRM
in Mailbox framework.

We don't have any IRQ for TX done so "txdone_irq" out of the question for
FlexRM. We only have completions for both success or failures (IO errors).

This means we have to use "txdone_poll" for FlexRM. For "txdone_poll",
we have to provide last_tx_done() callback. The last_tx_done() callback
is supposed to return true if last send_data() call succeeded.

To implement last_tx_done() in FlexRM driver, we added "last_pending_msg".

When "last_pending_msg" is NULL it means last call to send_data() succeeded
and when "last_pending_msg" is != NULL it means last call to send_data()
did not go through due to lack of space in FlexRM ring.

It could be simpler.
Since flexrm_send_data() is essentially about putting the message in
the ring-buffer (and not about _transmission_ failures), the
last_tx_done() should simply return true if requests_ida has not all
ids allocated. False otherwise.

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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.

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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.

The current implementation is trying to model FlexRM using "txdone_poll"
method and that's why we have dependency on MBOX_TX_QUEUE_LEN

I think what we really need is new method for "txdone" to model ring
manager HW (such as FlexRM). Let's call it "txdone_none".

For "txdone_none", it means there is no "txdone" reporting in HW
and mbox_send_data() should simply return value returned by
send_data() callback. The last_tx_done() callback is not required
for "txdone_none" and MBOX_TX_QUEUE_LEN also has no
effect on "txdone_none". Both blocking and non-blocking clients
are treated same for "txdone_none".

That is already supported :)

In drivers/dma/bcm-sba-raid.c

sba_send_mbox_request(...)
{
           ......
        req->msg.error = 0;
        ret = mbox_send_message(sba->mchans[mchans_idx], &req->msg);
        if (ret < 0) {
                dev_err(sba->dev, "send message failed with error %d", ret);
                return ret;
        }
        ret = req->msg.error;
        if (ret < 0) {
                dev_err(sba->dev, "message error %d", ret);
                return ret;
        }
          .....
}

Here you _do_ assume that as soon as the mbox_send_message() returns,
the last_tx_done() is true. In other words, this is a case of client
'knows_txdone'.

So ideally you should specify cl->knows_txdone = true during
mbox_request_channel() and have ...

sba_send_mbox_request(...)
{
        ret = mbox_send_message(sba->mchans[mchans_idx], &req->msg);
        if (ret < 0) {
                dev_err(sba->dev, "send message failed with error %d", ret);
                return ret;
        }

        ret = req->msg.error;

       /* Message successfully placed in the ringbuffer, i.e, done */
       mbox_client_txdone(sba->mchans[mchans_idx], ret);

       if (ret < 0) {
                dev_err(sba->dev, "message error %d", ret);
                return ret;
        }

        .....
}

This way MBOX_TX_QUEUE_LEN should be more than enough and pose no bottleneck.


Cheers!