From: Dmitry Osipenko <digetx@gmail.com>
To: Sowjanya Komatineni <skomatineni@nvidia.com>,
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
Subject: Re: [RFC PATCH v9 6/9] media: tegra: Add Tegra210 Video input driver
Date: Fri, 24 Apr 2020 05:09:00 +0300 [thread overview]
Message-ID: <5ad77b67-0dc6-3c6d-7df3-4c21c68b2b1e@gmail.com> (raw)
In-Reply-To: <8f01724e-95d4-e6d8-9e2d-bce4b8dd0177@nvidia.com>
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());
next prev parent reply other threads:[~2020-04-24 2:09 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-22 6:18 [RFC PATCH v9 0/9] Add Tegra driver for video capture Sowjanya Komatineni
2020-04-22 6:18 ` [RFC PATCH v9 1/9] arm64: tegra: Fix sor powergate clocks and reset Sowjanya Komatineni
2020-04-22 6:18 ` [RFC PATCH v9 2/9] arm64: tegra: Add reset-cells to mc Sowjanya Komatineni
2020-04-22 6:18 ` [RFC PATCH v9 3/9] dt-bindings: clock: tegra: Add clk id for CSI TPG clock Sowjanya Komatineni
2020-04-22 6:18 ` [RFC PATCH v9 4/9] clk: tegra: Add Tegra210 CSI TPG clock gate Sowjanya Komatineni
2020-04-22 6:18 ` [RFC PATCH v9 5/9] dt-binding: tegra: Add VI and CSI bindings Sowjanya Komatineni
2020-04-22 17:20 ` Laurent Pinchart
2020-04-22 17:26 ` Sowjanya Komatineni
2020-04-22 17:47 ` Laurent Pinchart
2020-04-22 17:57 ` Sowjanya Komatineni
2020-04-22 6:18 ` [RFC PATCH v9 6/9] media: tegra: Add Tegra210 Video input driver Sowjanya Komatineni
2020-04-23 7:48 ` Hans Verkuil
2020-04-23 16:50 ` Sowjanya Komatineni
2020-04-23 22:55 ` Dmitry Osipenko
2020-04-23 22:59 ` Sowjanya Komatineni
2020-04-23 23:03 ` Dmitry Osipenko
2020-04-23 23:14 ` Dmitry Osipenko
2020-04-23 23:16 ` Dmitry Osipenko
2020-04-23 23:19 ` Sowjanya Komatineni
2020-04-23 23:20 ` Sowjanya Komatineni
2020-04-23 23:25 ` Dmitry Osipenko
2020-04-23 23:50 ` Sowjanya Komatineni
2020-04-24 0:42 ` Dmitry Osipenko
2020-04-24 0:51 ` Sowjanya Komatineni
2020-04-24 1:08 ` Sowjanya Komatineni
2020-04-24 2:09 ` Dmitry Osipenko [this message]
2020-04-24 2:12 ` Sowjanya Komatineni
2020-04-22 6:18 ` [RFC PATCH v9 7/9] MAINTAINERS: Add Tegra Video driver section Sowjanya Komatineni
2020-04-22 6:18 ` [RFC PATCH v9 8/9] dt-bindings: reset: Add ID for Tegra210 VI reset Sowjanya Komatineni
2020-04-22 6:18 ` [RFC PATCH v9 9/9] arm64: tegra: Add Tegra VI CSI support in device tree Sowjanya Komatineni
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