linux-kernel - Re: [RFC PATCH v9 6/9] media: tegra: Add Tegra210 Video input driver

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Date:   Fri, 24 Apr 2020 03:42:05 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com, frankc@...dia.com,
        hverkuil@...all.nl, sakari.ailus@....fi, helen.koike@...labora.com
Cc:     sboyd@...nel.org, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v9 6/9] media: tegra: Add Tegra210 Video input driver

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.