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[23.128.96.18]) by mx.google.com with ESMTP id qc24si5659794ejb.398.2020.08.07.09.10.46; Fri, 07 Aug 2020 09:11:09 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=collabora.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726293AbgHGQIy (ORCPT + 99 others); Fri, 7 Aug 2020 12:08:54 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:48262 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725815AbgHGQIx (ORCPT ); Fri, 7 Aug 2020 12:08:53 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: dafna) with ESMTPSA id B0F42299512 Subject: Re: [PATCH v8 05/14] media: rkisp1: add Rockchip ISP1 subdev driver To: Tomasz Figa Cc: Laurent Pinchart , Helen Koike , "open list:ARM/Rockchip SoC..." , linux-devicetree , Eddie Cai , Mauro Carvalho Chehab , =?UTF-8?Q?Heiko_St=c3=bcbner?= , Chen Jacob , Jeffy , =?UTF-8?B?6ZKf5Lul5bSH?= , Linux Kernel Mailing List , Hans Verkuil , Sakari Ailus , kernel@collabora.com, Ezequiel Garcia , Linux Media Mailing List , "list@263.net:IOMMU DRIVERS" , Joerg Roedel , linux-arm-kernel@lists.infradead.org, Shunqian Zheng , Jacob Chen , Allon Huang References: <20190730184256.30338-1-helen.koike@collabora.com> <20190730184256.30338-6-helen.koike@collabora.com> <20190816001323.GF5011@pendragon.ideasonboard.com> <30b6367d-9088-d755-d041-904ff2a48130@collabora.com> <20200722152459.GC1828171@chromium.org> <32a95f66-0328-dfe7-c05c-657aba0d1b25@collabora.com> <05fb7b03-22b5-c981-2602-bbe877943d58@collabora.com> From: Dafna Hirschfeld Message-ID: <7c138a50-f167-c99e-3418-1927b36809fc@collabora.com> Date: Fri, 7 Aug 2020 18:08:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Am 06.08.20 um 14:22 schrieb Tomasz Figa: > On Thu, Aug 6, 2020 at 11:21 AM Dafna Hirschfeld > wrote: >> >> >> >> Am 05.08.20 um 23:10 schrieb Dafna Hirschfeld: >>> Hi >>> >>> On 22.07.20 17:24, Tomasz Figa wrote: >>>> Hi Dafna, >>>> >>>> On Sat, Jul 11, 2020 at 01:04:31PM +0200, Dafna Hirschfeld wrote: >>>>> Hi Laurent, >>>>> >>>>> On 16.08.19 02:13, Laurent Pinchart wrote: >>>>>> Hello Helen, >>>>>> >>>>>> Thank you for the patch. >>>>>> >>>>>> On Tue, Jul 30, 2019 at 03:42:47PM -0300, Helen Koike wrote: >>>> [snip] >>>>>>> +static void rkisp1_isp_queue_event_sof(struct rkisp1_isp_subdev *isp) >>>>>>> +{ >>>>>>> + struct v4l2_event event = { >>>>>>> + .type = V4L2_EVENT_FRAME_SYNC, >>>>>>> + .u.frame_sync.frame_sequence = >>>>>>> + atomic_inc_return(&isp->frm_sync_seq) - 1, >>>>>> >>>>>> I would move the increment to the caller, hiding it in this function is >>>>>> error-prone (and if you look at the caller I'm pointing out one possible >>>>>> error :-)). >>>>>> >>>>>> In general usage of frm_sync_seq through the driver seems to be very >>>>>> race-prone. It's read in various IRQ handling functions, all coming from >>>>>> the same IRQ, so that part is fine (and wouldn't require an atomic >>>>>> variable), but when read from the buffer queue handlers I really get a >>>>>> red light flashing in my head. I'll try to investigate more when >>>>>> reviewing the next patches. >>>>> >>>>> I see that the only place were 'frame_sequence' is read outside of the irq >>>>> handlers is in the capture in 'rkisp1_vb2_buf_queue': >>>>> >>>>> /* >>>>> * If there's no next buffer assigned, queue this buffer directly >>>>> * as the next buffer, and update the memory interface. >>>>> */ >>>>> if (cap->is_streaming && !cap->buf.next && >>>>> atomic_read(&cap->rkisp1->isp.frame_sequence) == -1) { >>>>> cap->buf.next = ispbuf; >>>>> rkisp1_set_next_buf(cap); >>>>> } else { >>>>> list_add_tail(&ispbuf->queue, &cap->buf.queue); >>>>> } >>>>> This "if" condition seems very specific, a case where we already stream but v-start was not yet received. >>>>> I think it is possible to remove the test 'atomic_read(&cap->rkisp1->isp.frame_sequence) == -1' >>>>> from the above condition so that the next buffer is updated in case it is null not just before the first >>>>> v-start signal. >>>>> >>>> >>>> We don't have this special case in the Chrome OS code. >>>> >>>> I suppose it would make it possible to resume the capture 1 frame >>>> earlier after a queue underrun, as otherwise the new buffer would be >>>> only programmed after the next frame start interrupt and used for the >>>> next-next frame. However, it's racy, because programming of the buffer >>>> addresses is not atomic and could end up with the hardware using few >>>> plane addresses from the new buffer and few from the dummy buffer. >>>> >>>> Given that and also the fact that a queue underrun is a very special >>>> case, where the system was already having problems catching up, I'd just >>>> remove this special case. >>>> >>>> [snip] >>>>>>> +void rkisp1_isp_isr(unsigned int isp_mis, struct rkisp1_device *dev) >>>>>>> +{ >>>>>>> + void __iomem *base = dev->base_addr; >>>>>>> + unsigned int isp_mis_tmp = 0; >>>>>> >>>>>> _tmp are never good names :-S >>>>>> >>>>>>> + unsigned int isp_err = 0; >>>>>> >>>>>> Neither of these variable need to be initialised to 0. >>>>>> >>>>>>> + >>>>>>> + /* start edge of v_sync */ >>>>>>> + if (isp_mis & CIF_ISP_V_START) { >>>>>>> + rkisp1_isp_queue_event_sof(&dev->isp_sdev); >>>>>> >>>>>> This will increment the frame sequence number. What if the interrupt is >>>>>> slightly delayed and the next frame starts before we get a change to >>>>>> copy the sequence number to the buffers (before they will complete >>>>>> below) ? >>>>> >>>>> Do you mean that we get two sequental v-start signals and then the next >>>>> frame-end signal in MI_MIS belongs to the first v-start signal of the two? >>>>> How can this be solved? I wonder if any v-start signal has a later signal >>>>> that correspond to the same frame so that we can follow it? >>>>> >>>>> Maybe we should have one counter that is incremented on v-start signal, >>>>> and another counter that is incremented uppon some other signal? >>>>> >>>> >>>> We're talking about a hard IRQ. I can't imagine the interrupt handler >>>> being delayed for a time close to a full frame interval (~16ms for 60 >>>> fps) to trigger such scenario. >>>> >>>>>> >>>>>>> + >>>>>>> + writel(CIF_ISP_V_START, base + CIF_ISP_ICR); >>>>>> >>>>>> Do you need to clear all interrupt bits individually, can't you write >>>>>> isp_mis to CIF_ISP_ICR at the beginning of the function to clear them >>>>>> all in one go ? >>>>>> >>>>>>> + isp_mis_tmp = readl(base + CIF_ISP_MIS); >>>>>>> + if (isp_mis_tmp & CIF_ISP_V_START) >>>>>>> + v4l2_err(&dev->v4l2_dev, "isp icr v_statr err: 0x%x\n", >>>>>>> + isp_mis_tmp); >>>>>> >>>>>> This require some explanation. It looks like a naive way to protect >>>>>> against something, but I think it could trigger under normal >>>>>> circumstances if IRQ handling is delayed, and wouldn't do much anyway. >>>>>> Same for the similar constructs below. >>>>>> >>>>>>> + } >>>>>>> + >>>>>>> + if ((isp_mis & CIF_ISP_PIC_SIZE_ERROR)) { >>>>>>> + /* Clear pic_size_error */ >>>>>>> + writel(CIF_ISP_PIC_SIZE_ERROR, base + CIF_ISP_ICR); >>>>>>> + isp_err = readl(base + CIF_ISP_ERR); >>>>>>> + v4l2_err(&dev->v4l2_dev, >>>>>>> + "CIF_ISP_PIC_SIZE_ERROR (0x%08x)", isp_err); >>>>>> >>>>>> What does this mean ? >>>>>> >>>>>>> + writel(isp_err, base + CIF_ISP_ERR_CLR); >>>>>>> + } else if ((isp_mis & CIF_ISP_DATA_LOSS)) { >>>>>> >>>>>> Are CIF_ISP_PIC_SIZE_ERROR and CIF_ISP_DATA_LOSS mutually exclusive ? >>>>>> >>>>>>> + /* Clear data_loss */ >>>>>>> + writel(CIF_ISP_DATA_LOSS, base + CIF_ISP_ICR); >>>>>>> + v4l2_err(&dev->v4l2_dev, "CIF_ISP_DATA_LOSS\n"); >>>>>>> + writel(CIF_ISP_DATA_LOSS, base + CIF_ISP_ICR); >>>>>>> + } >>>>>>> + >>>>>>> + /* sampled input frame is complete */ >>>>>>> + if (isp_mis & CIF_ISP_FRAME_IN) { >>>>>>> + writel(CIF_ISP_FRAME_IN, base + CIF_ISP_ICR); >>>>>>> + isp_mis_tmp = readl(base + CIF_ISP_MIS); >>>>>>> + if (isp_mis_tmp & CIF_ISP_FRAME_IN) >>>>>>> + v4l2_err(&dev->v4l2_dev, "isp icr frame_in err: 0x%x\n", >>>>>>> + isp_mis_tmp); >>>>>>> + } >>>>>>> + >>>>>>> + /* frame was completely put out */ >>>>>> >>>>>> "put out" ? :-) What's the difference between ISP_FRAME_IN and ISP_FRAME >>>>>> ? The two comments could do with a bit of brush up, and I think the >>>>>> ISP_FRAME_IN interrupt could be disabled as it doesn't perform any >>>>>> action. >>>>> >>>>> Those two oneline comments are just copy-paste from the datasheet. >>>>> >>>>> "" >>>>> 5 MIS_FRAME_IN sampled input frame is complete >>>>> 1 MIS_FRAME frame was completely put out >>>>> "" >>>>> >>>>> Unfrotunately, the datasheet does not add any further explanation about those signals. >>>>> >>>>> >>>> >>>> My loose recollection is that the former is signaled when then frame >>>> is fully input to the ISP and the latter when the ISP completes >>>> outputting the frame to the next block in the pipeline, but someone >>>> would need to verify this, for example by printing timestamps for all >>>> the various interrupts. >>>> >>>>>> >>>>>>> + if (isp_mis & CIF_ISP_FRAME) { >>>>>>> + u32 isp_ris = 0; >>>>>> >>>>>> No need to initialise this to 0. >>>>>> >>>>>>> + /* Clear Frame In (ISP) */ >>>>>>> + writel(CIF_ISP_FRAME, base + CIF_ISP_ICR); >>>>>>> + isp_mis_tmp = readl(base + CIF_ISP_MIS); >>>>>>> + if (isp_mis_tmp & CIF_ISP_FRAME) >>>>>>> + v4l2_err(&dev->v4l2_dev, >>>>>>> + "isp icr frame end err: 0x%x\n", isp_mis_tmp); >>>>>>> + >>>>>>> + isp_ris = readl(base + CIF_ISP_RIS); >>>>>>> + if (isp_ris & (CIF_ISP_AWB_DONE | CIF_ISP_AFM_FIN | >>>>>>> + CIF_ISP_EXP_END | CIF_ISP_HIST_MEASURE_RDY)) >>>>>>> + rkisp1_stats_isr(&dev->stats_vdev, isp_ris); >>>>>> >>>>>> Is there a guarantee that the statistics will be fully written out >>>>>> before the video frame itself ? And doesn't this test if any of the >>>>>> statistics is complete, not all of them ? I think the logic is wrong, it >>>>> >>>>> The datasheet does not add any explanation of what is expected to come first. >>>>> Should we wait until all statistics measurements are done? In the struct >>>>> sent to userspace there is a bitmaks for which of the statistics are read. >>>>> I think that if only part of the statistics are ready, we can already send the once >>>>> that are ready to userspace. >>>>> >>>> >>>> If we look further into the code, rkisp1_stats_isr() checks the >>>> interrupt status mask passed to it and reads out only the parameters >>>> with indicated completion. The statistics metadata buffer format >>>> includes a bit mask which tells the userspace which measurements are >>>> available. >>>> >>>> However, I think I've spotted a bug there. At the beginning of >>>> rkisp1_stats_isr(), all the 4 interrupt status bits are cleared, >>>> regardless of the mask used later to decide which readouts need to be >>>> done. This could mean that with an unfortunate timing, some measurements >>>> would be lost. So at least the code should be fixed to only clear the >>>> interrupts bits really handled. >>> >>> I'll fix that >> >> I actually don't think this is a bug. The statistics interrupts are not >> enabled and are read from the raw interrupts register. This means >> that if we missed a statistics for the current frame and we don't reset it >> then we will read it only when the next frame comes out, so it will be >> wrongly set as statistics for the next frame although it is actually for the >> current frame. > > Yes, I noticed that the driver attempts to reduce the number of > interrupts by assuming that the ISP statistics can be read after the > MIS_FRAME interrupt. However, in this case, I don't think we can ever > miss statistics for a frame (unless the system is broken and has > unacceptable interrupt latencies) nor the unfortunate timing I > suggested before could ever take place. So we actually don't even need the `meas_type` bitmask that tells which statistics are in in the struct. Should I send a patch removing it? Maybe just to be on the safe side I can add a WARNING in case not all statistics are ready or or at least a debugfs variable. Thanks, Dafna > > Best regards, > Tomasz > >> >> Thanks, >> Dafna >> >>> >>>> >>>> As for whether to send separate buffers for each measurement, I guess >>>> it's not a bad thing to let the userspace access the ones available >>>> earlier. Now I only don't recall why we decided to put all the >>>> measurements into one metadata structure, rather than splitting the 4 >>>> into their own structures and buffer queues... >>> >>> Is it possible to have several queues to the same video node? >>> >>>> >>>>>> seems it should be moved out of the CIF_ISP_FRAME test, to a test of its >>>>>> own. It's hard to tell for sure without extra information though (for >>>>>> instance why are the stats-related bits read from CIF_ISP_RIS, when >>>>>> they seem to be documented as valid in CIF_ISP_ISR), but this should be >>>>>> validated, and most probably fixed. Care should be taken to keep >>>>>> synchronisation of sequence number between the different queues. >>>>> >>>>> I see that the capture buffers are done before incrementing the frame_sequence with >>>>> the following explanation: >>>>> >>>>> /* >>>>> * Call rkisp1_capture_isr() first to handle the frame that >>>>> * potentially completed using the current frame_sequence number before >>>>> * it is potentially incremented by rkisp1_isp_isr() in the vertical >>>>> * sync. >>>>> */ >>>>> >>>>> I think reading the stats/params should also be done before calling rkisp1_capture_isr >>>>> for the same reason. (so to match the correct frame_sequence) >>>> >>>> My recollection of the sequence of interrupts in this hardware is like >>>> this: >>>> >>>> CIF_ISP_V_START (frame 0) >>>> CIF_ISP_FRAME_IN (frame 0) >>>> CIF_ISP_FRAME (frame 0) >>>> CIF_ISP_AWB_DONE >>>> CIF_ISP_AFM_FIN >>>> CIF_ISP_EXP_END >>>> CIF_ISP_HIST_MEASURE_RDY >>>> CIF_MI_FRAME* >>>> CIF_ISP_V_START (frame 1) >>>> CIF_ISP_FRAME_IN (frame 1) >>>> CIF_ISP_FRAME (frame 1) >>>> ... >>>> >>>> where the interrupts at the same indentation level can happen >>>> independently of each other. Again, someone would have to verify this. >>> >>> I wrote this patch to print the interrupts and the time difference between interrupts: >>> https://gitlab.collabora.com/dafna/linux/-/commit/9b9c5ddc2f06a6b87d2c1b210219f69de83296c5 >>> >>> I got this output: http://ix.io/2tl8, >>> there is a repeating pattern where only v-start interrupt is sent, indicated by the prints "isp mis 0x00000040" then about 23 milisec later are the other interrupts >>> (FRAME_IN, FRAME, MI_FRAME* ) and about 10 milisec the v-start interrupt again. >>> >>> I am still not sure why the mi_frame interrupt should be handled first. If it happen for example that all the interrupts arrive at once, how can >>> we know that the MI_FRAME interrupt relates to the previous v-start interrupt and not the current one? >>> I think that for that we need a code that keep track of the previous interrupt. >>> >>> Thanks, >>> Dafna >>> >>> >>>> >>>> Best regards, >>>> Tomasz >>>> >