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

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Message-ID: <a2672be9-93c1-8363-6c0e-6d43c2bd59bc@nvidia.com>
Date:   Thu, 23 Apr 2020 16:50:36 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.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


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.