linux-kernel - Re: [RFC PATCH v11 6/9] media: tegra: Add Tegra210 Video input driver

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Message-ID: <bfd82642-9648-96f1-737d-4b9a869d34a3@nvidia.com>
Date:   Thu, 30 Apr 2020 13:08:39 -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 v11 6/9] media: tegra: Add Tegra210 Video input driver


On 4/30/20 1:06 PM, Dmitry Osipenko wrote:
> 30.04.2020 01:00, 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;
>> +
>> +	set_freezable();
>> +
>> +	while (1) {
>> +		try_to_freeze();
>> +
>> +		/*
>> +		 * Source is not streaming if error is non-zero.
>> +		 * So, do not dequeue buffers on error and let the thread sleep
>> +		 * till kthread stop signal is received.
>> +		 */
>> +		wait_event_interruptible(chan->start_wait,
>> +					 kthread_should_stop() ||
>> +					 (!list_empty(&chan->capture) &&
>> +					 !err));
> ...
>> +static void tegra_channel_buffer_queue(struct vb2_buffer *vb)
>> +{
>> +	struct tegra_vi_channel *chan = vb2_get_drv_priv(vb->vb2_queue);
>> +	struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb);
>> +	struct tegra_channel_buffer *buf = to_tegra_channel_buffer(vbuf);
>> +
>> +	/* put buffer into the capture queue */
>> +	spin_lock(&chan->start_lock);
>> +	list_add_tail(&buf->queue, &chan->capture);
>> +	spin_unlock(&chan->start_lock);
>> +
>> +	/* wait up kthread for capture */
>> +	wake_up_interruptible(&chan->start_wait);
>> +}
> The V4L doc says that buffers could be enqueued before streaming is
> started. I guess it should be a trouble here, shouldn't it?
>
> https://elixir.bootlin.com/linux/v5.7-rc3/source/include/media/videobuf2-core.h#L379

what trouble are you referring here?

I dont think so as we set min buffers needed as 2 always there will be 2 
per-queued buffers.

But buffers from this queue will be dequeued only when ready to 
processes in the capture thread