Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751776AbdG1Itw (ORCPT ); Fri, 28 Jul 2017 04:49:52 -0400 Received: from mail-ua0-f173.google.com ([209.85.217.173]:36600 "EHLO mail-ua0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751007AbdG1Itu (ORCPT ); Fri, 28 Jul 2017 04:49:50 -0400 MIME-Version: 1.0 In-Reply-To: References: <1500620142-910-1-git-send-email-anup.patel@broadcom.com> <1500620142-910-7-git-send-email-anup.patel@broadcom.com> From: Anup Patel Date: Fri, 28 Jul 2017 14:19:48 +0530 Message-ID: Subject: Re: [PATCH v2 6/7] mailbox: bcm-flexrm-mailbox: Set msg_queue_len for each channel To: Jassi Brar Cc: Rob Herring , Mark Rutland , Catalin Marinas , Will Deacon , Florian Fainelli , Scott Branden , Ray Jui , Linux Kernel Mailing List , "linux-arm-kernel@lists.infradead.org" , Devicetree List , BCM Kernel Feedback Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8984 Lines: 209 On Thu, Jul 27, 2017 at 5:23 PM, Jassi Brar wrote: > On Thu, Jul 27, 2017 at 11:20 AM, Anup Patel wrote: >> On Thu, Jul 27, 2017 at 10:29 AM, Jassi Brar wrote: > >>>>>>>> Sorry for the delayed response... >>>>>>>> >>>>>>>> On Fri, Jul 21, 2017 at 9:16 PM, Jassi Brar wrote: >>>>>>>>> Hi Anup, >>>>>>>>> >>>>>>>>> On Fri, Jul 21, 2017 at 12:25 PM, Anup Patel 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 >>>>>>>>>> Reviewed-by: Scott Branden >>>>>>>>>> --- >>>>>>>>>> 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. It's not that simple because we have two cases in-which send_data() will fail: 1. It run-out of IDs in requests_ida 2. There is no room in BD queue of FlexRM ring. This because each brcm_message can be translated into variable number of descriptors. In fact, using SPU2 crypto client we have one brcm_message translating into 100's of descriptors. All-in-all few messages (< 1024) can also fill-up the BD queue of FlexRM ring. > >>> >>> 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. >> >> 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 :) If you are referring to "txdone_ack" then this cannot be used here because for "txdone_ack" we have to call mbox_chan_txdon() API after writing descriptors in send_data() callback which will cause dead-lock in tx_tick() called by mbox_chan_txdone(). > > 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; > } > > ..... > } > I think we need to improve mailbox.c so that mbox_chan_txdone() can be called from send_data() callback. Regards, Anup