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

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Message-ID: <52b98347-4b78-f637-04f4-cc730ad336f3@nvidia.com>
Date:   Thu, 30 Apr 2020 13:09:57 -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 1:08 PM, Sowjanya Komatineni wrote:
>
> 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.
typo* pre-queued buffers before streaming start
>
> But buffers from this queue will be dequeued only when ready to 
> processes in the capture thread
>