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Subject: Re: [RFC PATCH v11 6/9] media: tegra: Add Tegra210 Video input driver
To:     Dmitry Osipenko <digetx@gmail.com>, <thierry.reding@gmail.com>,
        <jonathanh@nvidia.com>, <frankc@nvidia.com>, <hverkuil@xs4all.nl>,
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From:   Sowjanya Komatineni <skomatineni@nvidia.com>
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Date:   Thu, 30 Apr 2020 13:21:15 -0700
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On 4/30/20 1:21 PM, Dmitry Osipenko wrote:
> 30.04.2020 23:09, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>> 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 =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>>>> +static int chan_capture_kthread_start(void *data)
>>>>> +{
>>>>> +=C2=A0=C2=A0=C2=A0 struct tegra_vi_channel *chan =3D data;
>>>>> +=C2=A0=C2=A0=C2=A0 struct tegra_channel_buffer *buf;
>>>>> +=C2=A0=C2=A0=C2=A0 int err =3D 0;
>>>>> +
>>>>> +=C2=A0=C2=A0=C2=A0 set_freezable();
>>>>> +
>>>>> +=C2=A0=C2=A0=C2=A0 while (1) {
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 try_to_freeze();
>>>>> +
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /*
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * Source is not str=
eaming if error is non-zero.
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * So, do not dequeu=
e buffers on error and let the thread
>>>>> sleep
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * till kthread stop=
 signal is received.
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 wait_event_interruptible(=
chan->start_wait,
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kthread_should_stop(=
) ||
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (!list_empty(&chan->=
capture) &&
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 !err));
>>>> ...
>>>>> +static void tegra_channel_buffer_queue(struct vb2_buffer *vb)
>>>>> +{
>>>>> +=C2=A0=C2=A0=C2=A0 struct tegra_vi_channel *chan =3D vb2_get_drv_pri=
v(vb->vb2_queue);
>>>>> +=C2=A0=C2=A0=C2=A0 struct vb2_v4l2_buffer *vbuf =3D to_vb2_v4l2_buff=
er(vb);
>>>>> +=C2=A0=C2=A0=C2=A0 struct tegra_channel_buffer *buf =3D to_tegra_cha=
nnel_buffer(vbuf);
>>>>> +
>>>>> +=C2=A0=C2=A0=C2=A0 /* put buffer into the capture queue */
>>>>> +=C2=A0=C2=A0=C2=A0 spin_lock(&chan->start_lock);
>>>>> +=C2=A0=C2=A0=C2=A0 list_add_tail(&buf->queue, &chan->capture);
>>>>> +=C2=A0=C2=A0=C2=A0 spin_unlock(&chan->start_lock);
>>>>> +
>>>>> +=C2=A0=C2=A0=C2=A0 /* wait up kthread for capture */
>>>>> +=C2=A0=C2=A0=C2=A0 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/videobu=
f2-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.
ok. yes threads run only during streaming