Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751965AbdG1Jsc (ORCPT ); Fri, 28 Jul 2017 05:48:32 -0400 Received: from mail-ua0-f181.google.com ([209.85.217.181]:33419 "EHLO mail-ua0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751674AbdG1Jsa (ORCPT ); Fri, 28 Jul 2017 05:48:30 -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 15:18:27 +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: 10621 Lines: 243 On Fri, Jul 28, 2017 at 2:34 PM, Jassi Brar wrote: > 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. Let say at time T, there was no space in BD queue. Now at time T+X when last_tx_done() it is possible that BD queue has space because FlexRM has processed some more descriptor. I think last_tx_done() for "txdone_poll" method will require some information passing from send_data() callback to last_tx_done() which is last_pending_msg for FlexRM driver. Anyways, I plan to try "txdone_ack" method so I will remove last_tx_done() and last_pending_msg both. What do you think? > > >>>>> >>>>> 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 OK so I got confused between mbox_chan_txdone() and mbox_client_txdone(). We should do mbox_client_txdone() from mailbox client when mbox_chan txmethod is ACK. Regards, Anup