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

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Message-ID: <7d31d24f-f353-7e82-3ff9-cdba8b773d1e@nvidia.com>
Date:   Thu, 30 Apr 2020 09:29:00 -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 9:04 AM, Sowjanya Komatineni wrote:
>
> On 4/30/20 7:13 AM, Dmitry Osipenko wrote:
>> 30.04.2020 17:02, Dmitry Osipenko пишет:
>>> 30.04.2020 16:56, Dmitry Osipenko пишет:
>>>> 30.04.2020 01:00, Sowjanya Komatineni пишет:
>>>>> +static int chan_capture_kthread_finish(void *data)
>>>>> +{
>>>>> +    struct tegra_vi_channel *chan = data;
>>>>> +    struct tegra_channel_buffer *buf;
>>>>> +
>>>>> +    set_freezable();
>>>>> +
>>>>> +    while (1) {
>>>>> +        try_to_freeze();
>>>> I guess it won't be great to freeze in the middle of a capture 
>>>> process, so:
>>>>         if (list_empty(&chan->done))
>>>>             try_to_freeze();
>>> And here should be some locking protection in order not race with the
>>> chan_capture_kthread_start because kthread_finish could freeze before
>>> kthread_start.
>> Or maybe both start / finish threads should simply be allowed to freeze
>> only when both capture and done lists are empty.
>>
>> if (list_empty(&chan->capture) &&
>>      list_empty(&chan->done))
>>     try_to_freeze();
>
> good to freeze when not in middle of the frame capture but why should 
> we not allow freeze in between captures?
>
> Other drivers do allow freeze in between frame captures.
>
> I guess we can freeze before dequeue for capture and in finish thread 
> we can freeze after capture done. This also don't need to check for 
> list_empty with freeze to allow between frame captures.
>
Also if we add check for both lists empty, freeze is not allowed as long 
as streaming is going on and in case of continuous streaming freeze will 
never happen.