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

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Message-ID: <d9aa7cb7-cb16-9896-17c9-2d84fbaa0893@nvidia.com>
Date:   Thu, 30 Apr 2020 13:21:15 -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 1:21 PM, Dmitry Osipenko wrote:
> 30.04.2020 23:09, Sowjanya Komatineni пишет:
>> 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
> I see now that the threads won't be running until start_streaming() is
> invoked, should be okay then.
ok. yes threads run only during streaming