From: Sowjanya Komatineni <skomatineni@nvidia.com>
To: Dmitry Osipenko <digetx@gmail.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: Thu, 23 Apr 2020 19:12:07 -0700 [thread overview]
Message-ID: <8c8c0154-f790-f90f-e117-0d3df6823f20@nvidia.com> (raw)
In-Reply-To: <5ad77b67-0dc6-3c6d-7df3-4c21c68b2b1e@gmail.com>
On 4/23/20 7:09 PM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 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());
ok, will add err to wait condition to let it sleep
next prev parent reply other threads:[~2020-04-24 2:12 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
2020-04-24 2:12 ` Sowjanya Komatineni [this message]
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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