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[91.78.208.152]) by smtp.googlemail.com with ESMTPSA id l26sm3153517ljc.49.2020.04.23.19.09.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Apr 2020 19:09:02 -0700 (PDT) Subject: Re: [RFC PATCH v9 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: <1587536339-4030-1-git-send-email-skomatineni@nvidia.com> <1587536339-4030-7-git-send-email-skomatineni@nvidia.com> <7e473fa9-0409-d868-e818-2e7928a8acca@gmail.com> <3691c4b5-1ecc-2ad3-23ed-72ef6b8d25fa@nvidia.com> <492dafac-42aa-3caf-4d32-ba0e434b19c3@gmail.com> <39402a49-f39f-256c-31e7-afaa25d55664@nvidia.com> <8f01724e-95d4-e6d8-9e2d-bce4b8dd0177@nvidia.com> From: Dmitry Osipenko Message-ID: <5ad77b67-0dc6-3c6d-7df3-4c21c68b2b1e@gmail.com> Date: Fri, 24 Apr 2020 05:09:00 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <8f01724e-95d4-e6d8-9e2d-bce4b8dd0177@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 24.04.2020 04:08, Sowjanya Komatineni пишет: > > On 4/23/20 5:51 PM, Sowjanya Komatineni wrote: >> >> On 4/23/20 5:42 PM, Dmitry Osipenko wrote: >>> External email: Use caution opening links or attachments >>> >>> >>> 24.04.2020 02:50, Sowjanya Komatineni пишет: >>>> On 4/23/20 4:25 PM, Dmitry Osipenko wrote: >>>>> External email: Use caution opening links or attachments >>>>> >>>>> >>>>> 24.04.2020 02:20, Sowjanya Komatineni пишет: >>>>>> On 4/23/20 4:19 PM, Sowjanya Komatineni wrote: >>>>>>> On 4/23/20 4:16 PM, Dmitry Osipenko wrote: >>>>>>>> External email: Use caution opening links or attachments >>>>>>>> >>>>>>>> >>>>>>>> 22.04.2020 09:18, Sowjanya Komatineni пишет: >>>>>>>>> +static int chan_capture_kthread_start(void *data) >>>>>>>>> +{ >>>>>>>>> +     struct tegra_vi_channel *chan = data; >>>>>>>>> +     struct tegra_channel_buffer *buf; >>>>>>>>> +     int err = 0; >>>>>>>>> + >>>>>>>>> +     set_freezable(); >>>>>>>>> + >>>>>>>>> +     while (1) { >>>>>>>>> +             try_to_freeze(); >>>>>>>>> + >>>>>>>>> + wait_event_interruptible(chan->start_wait, >>>>>>>>> + !list_empty(&chan->capture) || >>>>>>>>> + kthread_should_stop()); >>>>>>>>> + >>>>>>>>> +             if (kthread_should_stop()) >>>>>>>>> +                     break; >>>>>>>>> + >>>>>>>>> +             /* >>>>>>>>> +              * Source is not streaming if error is non-zero. >>>>>>>>> +              * So, do not dequeue buffers on capture error. >>>>>>>>> +              */ >>>>>>>>> +             if (err) >>>>>>>>> +                     continue; >>>>>>>> This will result in an endless loop, I suppose it wasn't the >>>>>>>> intention. >>>>>>> no it will not. on error we report vb2_queue_error which will do >>>>>>> streaming stop request. >>>>>>> >>>>>>> So thread will be stopped on streaming stop request thru kthread >>>>>>> stop >>>>>>> signal >>>>>> To be clear on error it reports vb2 queue error and waits for stop >>>>>> streaming to happen >>>>> If thread should exit on error, then it should do it on the actual >>>>> error. Otherwise it looks very error-prone. >>>> When v4l2 drivers indicate fatal error through vb2_queue_error, queue >>>> error flag  is set and wakes up all processes waiting on queue along >>>> with polling reporting  EPOLLERR and also reporting error for queuing >>>> and dequeuing buffers. Stream stop will surely happen which stops the >>>> thread. >>> This doesn't explain what is the point of continuing to loop instead of >>> exiting immediately on error. >> >> We are using 2 threads and when capture start error happens, we can >> stop capture_start thread immediately but capture_finish thread will >> still run for any outstanding buffers. >> >> So, as it makes no diff stopping both threads during stream stop which >> will definitely happen on error and when we don't dequeue buffers >> > Also there will be an issue if we break on error immediately during > stop_streaming -> kthread_stop() > > As stop streaming can happen any time, we do kthread_stop and in case of > error if we stop thread and on stop streaming kthread_stop might crash > as kthread_stop can only be called on running thread > This a better explanation, but still it's not good that there could be a busy loop within the thread. Should be better to sleep if error is set. wait_event_interruptible(chan->start_wait, (!err && !list_empty(&chan->capture)) || kthread_should_stop());