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

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Date:   Mon, 6 Apr 2020 13:55:12 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.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


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