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Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver
To:     Dmitry Osipenko <digetx@gmail.com>, <thierry.reding@gmail.com>,
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From:   Sowjanya Komatineni <skomatineni@nvidia.com>
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On 4/6/20 1:56 PM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 06.04.2020 23:55, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>> On 4/6/20 1:53 PM, Dmitry Osipenko wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> 06.04.2020 23:50, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>>> On 4/6/20 1:45 PM, Dmitry Osipenko wrote:
>>>>> External email: Use caution opening links or attachments
>>>>>
>>>>>
>>>>> 04.04.2020 04:25, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>>>>> +static int chan_capture_kthread_start(void *data)
>>>>>> +{
>>>>>> +     struct tegra_vi_channel *chan =3D data;
>>>>>> +     struct tegra_channel_buffer *buf;
>>>>>> +     int err =3D 0;
>>>>>> +     int caps_inflight;
>>>>>> +
>>>>>> +     set_freezable();
>>>>>> +
>>>>>> +     while (1) {
>>>>>> +             try_to_freeze();
>>>>>> +
>>>>>> +             wait_event_interruptible(chan->start_wait,
>>>>>> +                                      !list_empty(&chan->capture) |=
|
>>>>>> +                                      kthread_should_stop());
>>>>>> +             /*
>>>>>> +              * Frame start and MW_ACK_DONE syncpoint condition
>>>>>> FIFOs are
>>>>>> +              * of max depth 2. So make sure max 2 capture
>>>>>> requests are
>>>>>> +              * in process by the hardware at a time.
>>>>>> +              */
>>>>>> +             while (!(kthread_should_stop() ||
>>>>>> list_empty(&chan->capture))) {
>>>>>> +                     caps_inflight =3D chan->capture_reqs -
>>>>>> chan->sequence;
>>>>>> +                     /*
>>>>>> +                      * Source is not streaming if error is non-zer=
o.
>>>>>> +                      * So, do not dequeue buffers on capture error
>>>>>> or when
>>>>>> +                      * syncpoint requests in FIFO are full.
>>>>>> +                      */
>>>>>> +                     if (err || caps_inflight >=3D SYNCPT_FIFO_DEPT=
H)
>>>>>> +                             break;
>>>>> Am I understanding correctly that this thread will take 100% CPU,
>>>>> spinning here, if more than 2 frame-captures queued?
>>>> on more than 2 frames captures, it breaks thread and on next wakeup it
>>>> continues
>>> The wait_event() won't wait if condition is true.
>> condition is checked when waitqueue is woken up
> https://elixir.bootlin.com/linux/v5.6.2/source/include/linux/wait.h#L462

process is put to sleep until the condition evaluates to true or signal=20
is received.

condition is checked each time the waitqueue head is woken up.

Also capture list may keep on getting updated with buffers from userspace.

but at a time we only limit 2 frames as VI supports double buffering and=20
syncpt fifo's max depth is 2

Any more buffers waiting will be processing on subsequent iterations.

So basically thread run time is depending on buffers getting queued from=20
userspace.