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[91.78.208.152]) by smtp.googlemail.com with ESMTPSA id 64sm10460457ljj.41.2020.04.06.12.53.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Apr 2020 12:53:52 -0700 (PDT) Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver To: Sowjanya Komatineni , thierry.reding@gmail.com, jonathanh@nvidia.com, frankc@nvidia.com, hverkuil@xs4all.nl, sakari.ailus@iki.fi, helen.koike@collabora.com Cc: sboyd@kernel.org, linux-media@vger.kernel.org, devicetree@vger.kernel.org, linux-clk@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <1585963507-12610-1-git-send-email-skomatineni@nvidia.com> <1585963507-12610-7-git-send-email-skomatineni@nvidia.com> <38d921a7-5cdf-8d0a-2772-4399dd1a96a0@gmail.com> <9b8cf37b-d2ad-9df2-aad8-216c2c954e69@nvidia.com> <1a12974a-7cc7-2c3a-3995-076b9956714d@gmail.com> <66cc8646-43d3-3fc8-c31d-d0d2efac505f@nvidia.com> <9038ce90-ac53-93e7-ce65-57f6ff1e9b30@nvidia.com> From: Dmitry Osipenko Message-ID: Date: Mon, 6 Apr 2020 22:53:51 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <9038ce90-ac53-93e7-ce65-57f6ff1e9b30@nvidia.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org 06.04.2020 20:02, Sowjanya Komatineni пишет: > > On 4/6/20 9:37 AM, Sowjanya Komatineni wrote: >> >> On 4/6/20 9:29 AM, Dmitry Osipenko wrote: >>> External email: Use caution opening links or attachments >>> >>> >>> 06.04.2020 19:12, Sowjanya Komatineni пишет: >>>> On 4/6/20 9:05 AM, Dmitry Osipenko wrote: >>>>> External email: Use caution opening links or attachments >>>>> >>>>> >>>>> 06.04.2020 18:35, Sowjanya Komatineni пишет: >>>>> ... >>>>>>>> +     /* wait for syncpt counter to reach frame start event >>>>>>>> threshold */ >>>>>>>> +     err = host1x_syncpt_wait(chan->frame_start_sp, thresh, >>>>>>>> + TEGRA_VI_SYNCPT_WAIT_TIMEOUT, &value); >>>>>>>> +     if (err) { >>>>>>>> +             dev_err(&chan->video.dev, >>>>>>>> +                     "frame start syncpt timeout: %d\n", err); >>>>>>>> +             /* increment syncpoint counter for timedout events */ >>>>>>>> + host1x_syncpt_incr(chan->frame_start_sp); >>>>>>> Why incrementing is done while hardware is still active? >>>>>>> >>>>>>> The sync point's state needs to be completely reset after resetting >>>>>>> hardware. But I don't think that the current upstream host1x driver >>>>>>> supports doing that, it's one of the known-long-standing problems of >>>>>>> the >>>>>>> host1x driver. >>>>>>> >>>>>>> At least the sp->max_val incrementing should be done based on the >>>>>>> actual >>>>>>> syncpoint value and this should be done after resetting hardware. >>>>>> upstream host1x driver don't have API to reset or to equalize max >>>>>> value >>>>>> with min/load value. >>>>>> >>>>>> So to synchronize missed event, incrementing HW syncpt counter. >>>>>> >>>>>> This should not impact as we increment this in case of missed events >>>>>> only. >>>>> It's wrong to touch sync point while hardware is active and it's >>>>> active >>>>> until being reset. >>>>> >>>>> You should re-check the timeout after hw resetting and manually put >>>>> the >>>>> syncpoint counter back into sync only if needed. >>>> There is possibility of timeout to happen any time even during the >>>> capture also and is not related to hw reset. >>>> >>>> Manual synchronization is needed when timeout of any frame events >>>> happen >>>> otherwise all subsequence frames will timeout due to mismatch in event >>>> counters. >>> My point is that hardware is stopped only after being reset, until then >>> you should assume that sync point could be incremented by HW at any >>> time. >>> >>> And if this happens that HW increments sync point after the timeout, >>> then the sync point counter should become out-of-sync in yours case, >>> IIUC. Because host1x_syncpt_incr() doesn't update the cached counter. >> >> We wait for enough time based on frame rate for syncpt increment to >> happen and if it doesn't happen by then definitely its missed event >> and we increment HW syncpoint for this timed event. >> >> cached value gets updated during syncpt wait for subsequent event. >> >> syncpt increment happens for all subsequent frame events during video >> capture. >> > Just to be clear, syncpt max value increment happens first and syncpt > trigger condition is programmed. hw syncpt increment happens based on HW > events. > > Wait time for HW syncpt to reach threshold is tuned to work for all > frame rates. So if increment doesn't happen by then, its definitely > missed event. This is questionable. Technically, speculating about whether the tuned value is good for all possible cases is incorrect thing to do. Although, I guess in practice it should be good enough for the starter and could be improved later on, once the host1x driver will be improved. > In case of missed HW event corresponding to syncpt condition, hw syncpt > increment does not happen and driver increments it on timeout. > > As there is not API to equialize max with min incase of timeout/reset, > incrementing HW syncpt for timed out event. > > syncpt cached value gets updated during syncpt wait when it loads from > HW syncpt. > > As syncpt condition is already triggered, without compensating timeout > events or leaving syncpt max and hw syncpt in non synchronized state for > missed events, subsequent streamings will all timeout even on real events. >