linux-kernel - Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver

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Date:   Mon, 6 Apr 2020 23:56:28 +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 v6 6/9] media: tegra: Add Tegra210 Video input driver

06.04.2020 23:55, Sowjanya Komatineni пишет:
> 
> 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 пишет:
>>> 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 пишет:
>>>>> +static int chan_capture_kthread_start(void *data)
>>>>> +{
>>>>> +     struct tegra_vi_channel *chan = data;
>>>>> +     struct tegra_channel_buffer *buf;
>>>>> +     int err = 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 = chan->capture_reqs -
>>>>> chan->sequence;
>>>>> +                     /*
>>>>> +                      * Source is not streaming if error is non-zero.
>>>>> +                      * So, do not dequeue buffers on capture error
>>>>> or when
>>>>> +                      * syncpoint requests in FIFO are full.
>>>>> +                      */
>>>>> +                     if (err || caps_inflight >= SYNCPT_FIFO_DEPTH)
>>>>> +                             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