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

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Date:   Mon, 6 Apr 2020 23:53:31 +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 23:50, 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.