Messages in this thread | | | Subject | Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver | From | Sowjanya Komatineni <> | Date | Mon, 6 Apr 2020 13:20:46 -0700 |
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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; >> +}
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