Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751574AbdG0Dzc (ORCPT ); Wed, 26 Jul 2017 23:55:32 -0400 Received: from mail-ua0-f179.google.com ([209.85.217.179]:32935 "EHLO mail-ua0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751471AbdG0Dza (ORCPT ); Wed, 26 Jul 2017 23:55:30 -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: Thu, 27 Jul 2017 09:25:28 +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: 4295 Lines: 94 On Tue, Jul 25, 2017 at 9:37 PM, Jassi Brar wrote: > On Tue, Jul 25, 2017 at 11:11 AM, Anup Patel wrote: >> On Mon, Jul 24, 2017 at 10:06 PM, Jassi Brar wrote: >>> On Mon, Jul 24, 2017 at 9:26 AM, Anup Patel wrote: >>>> Hi Jassi, >>>> >>>> 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. >> >>> 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? > > 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. Regards, Anup