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

Sowjanya Komatineni
2020-04-06T20:20:50Z

On 4/6/20 1:02 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());
> Is it really okay that list_empty() isn't protected with a lock?
>
> Why wait_event is "interruptible"?

To allow it to sleep until wakeup on thread it to avoid constant
checking for condition even when no buffers are ready, basically to
prevent blocking.

>
>> + /*
>> + * 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;
>> +
>> + /* dequeue the buffer and start capture */
>> + spin_lock(&chan->start_lock);
>> + if (list_empty(&chan->capture))
>> + break;
>> + buf = list_entry(chan->capture.next,
>> + struct tegra_channel_buffer, queue);
> list_first_entry()
>
>> + list_del_init(&buf->queue);
>> + spin_unlock(&chan->start_lock);
>> +
>> + err = tegra_channel_capture_frame(chan, buf);
>> + if (err)
>> + vb2_queue_error(&chan->queue);
>> + }
>> +
>> + if (kthread_should_stop())
>> + break;
>> + }
>> +
>> + return 0;
>> +}