From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sowjanya Komatineni Subject: Re: [RFC PATCH v9 6/9] media: tegra: Add Tegra210 Video input driver Date: Thu, 23 Apr 2020 18:08:27 -0700 Message-ID: <8f01724e-95d4-e6d8-9e2d-bce4b8dd0177@nvidia.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <39402a49-f39f-256c-31e7-afaa25d55664-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Content-Language: en-US Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Dmitry Osipenko , thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, frankc-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, hverkuil-qWit8jRvyhVmR6Xm/wNWPw@public.gmane.org, sakari.ailus-X3B1VOXEql0@public.gmane.org, helen.koike-ZGY8ohtN/8qB+jHODAdFcQ@public.gmane.org Cc: sboyd-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, linux-media-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-clk-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-tegra@vger.kernel.org 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 =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>> 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 =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>>> 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 =D0=BF=D0=B8=D1=88=D0=B5=D1= =82: >>>>>>>> +static int chan_capture_kthread_start(void *data) >>>>>>>> +{ >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 struct tegra_vi_channel *chan =3D data; >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 struct tegra_channel_buffer *buf; >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 int err =3D 0; >>>>>>>> + >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 set_freezable(); >>>>>>>> + >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 while (1) { >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 try_to_freeze(); >>>>>>>> + >>>>>>>> + wait_event_interruptible(chan->start_wait, >>>>>>>> + !list_empty(&chan->capture) || >>>>>>>> + kthread_should_stop()); >>>>>>>> + >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 if (kthread_should_stop()) >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 break; >>>>>>>> + >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 /* >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 * Source is not streaming if error is non-zero. >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 * So, do not dequeue buffers on capture error. >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 */ >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 if (err) >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 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=20 >>>>>> 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=C2=A0 is set and wakes up all processes waiting on queue alo= ng >>> with polling reporting=C2=A0 EPOLLERR and also reporting error for queu= ing >>> 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=20 > stop capture_start thread immediately but capture_finish thread will=20 > still run for any outstanding buffers. > > So, as it makes no diff stopping both threads during stream stop which=20 > 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=20 stop_streaming -> kthread_stop() As stop streaming can happen any time, we do kthread_stop and in case of=20 error if we stop thread and on stop streaming kthread_stop might crash=20 as kthread_stop can only be called on running thread