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Subject: Re: [RFC PATCH v11 6/9] media: tegra: Add Tegra210 Video input driver
To:     Sowjanya Komatineni <skomatineni@nvidia.com>,
        thierry.reding@gmail.com, jonathanh@nvidia.com, frankc@nvidia.com,
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        linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org
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From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <8da0929d-4a58-75b8-381c-511ce66f8d9d@gmail.com>
Date:   Thu, 30 Apr 2020 23:21:07 +0300
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30.04.2020 23:09, Sowjanya Komatineni пишет:
> 
> On 4/30/20 1:08 PM, Sowjanya Komatineni wrote:
>>
>> On 4/30/20 1:06 PM, Dmitry Osipenko wrote:
>>> 30.04.2020 01:00, 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();
>>>> +
>>>> +        /*
>>>> +         * Source is not streaming if error is non-zero.
>>>> +         * So, do not dequeue buffers on error and let the thread
>>>> sleep
>>>> +         * till kthread stop signal is received.
>>>> +         */
>>>> +        wait_event_interruptible(chan->start_wait,
>>>> +                     kthread_should_stop() ||
>>>> +                     (!list_empty(&chan->capture) &&
>>>> +                     !err));
>>> ...
>>>> +static void tegra_channel_buffer_queue(struct vb2_buffer *vb)
>>>> +{
>>>> +    struct tegra_vi_channel *chan = vb2_get_drv_priv(vb->vb2_queue);
>>>> +    struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb);
>>>> +    struct tegra_channel_buffer *buf = to_tegra_channel_buffer(vbuf);
>>>> +
>>>> +    /* put buffer into the capture queue */
>>>> +    spin_lock(&chan->start_lock);
>>>> +    list_add_tail(&buf->queue, &chan->capture);
>>>> +    spin_unlock(&chan->start_lock);
>>>> +
>>>> +    /* wait up kthread for capture */
>>>> +    wake_up_interruptible(&chan->start_wait);
>>>> +}
>>> The V4L doc says that buffers could be enqueued before streaming is
>>> started. I guess it should be a trouble here, shouldn't it?
>>>
>>> https://elixir.bootlin.com/linux/v5.7-rc3/source/include/media/videobuf2-core.h#L379
>>>
>>
>> what trouble are you referring here?
>>
>> I dont think so as we set min buffers needed as 2 always there will be
>> 2 per-queued buffers.
> typo* pre-queued buffers before streaming start
>>
>> But buffers from this queue will be dequeued only when ready to
>> processes in the capture thread

I see now that the threads won't be running until start_streaming() is
invoked, should be okay then.