Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751726AbdG1JES (ORCPT ); Fri, 28 Jul 2017 05:04:18 -0400 Received: from mail-wm0-f53.google.com ([74.125.82.53]:38840 "EHLO mail-wm0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751465AbdG1JEQ (ORCPT ); Fri, 28 Jul 2017 05:04:16 -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: Jassi Brar Date: Fri, 28 Jul 2017 14:34:13 +0530 Message-ID: Subject: Re: [PATCH v2 6/7] mailbox: bcm-flexrm-mailbox: Set msg_queue_len for each channel To: Anup Patel 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: 9670 Lines: 221 On Fri, Jul 28, 2017 at 2:19 PM, Anup Patel wrote: > 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. > OK let me put it abstractly... return false if "there is no space for another message in the ringbuffer", true otherwise. >>>> >>>> 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(). > Did you read my code snippet below? It's not mbox_chan_txdone(), but mbox_client_txdone() which is called by the client. >> >> 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. > No please. Other clients call mbox_send_message() followed by mbox_client_txdone(), and they are right. For example, drivers/firmware/tegra/bpmp.c Thanks.