[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 [off-list ref] wrote:

On Tue, Jul 25, 2017 at 9:37 PM, Jassi Brar [off-list ref] wrote:

quoted

On Tue, Jul 25, 2017 at 11:11 AM, Anup Patel [off-list ref] wrote:

quoted

On Mon, Jul 24, 2017 at 10:06 PM, Jassi Brar [off-list ref] wrote:

quoted

On Mon, Jul 24, 2017 at 9:26 AM, Anup Patel [off-list ref] wrote:

quoted

Hi Jassi,

Sorry for the delayed response...

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

quoted

Hi Anup,

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

quoted

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?

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.

quoted

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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.

quoted

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.