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

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Date:   Thu, 30 Apr 2020 12:09:23 -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 11:18 AM, Sowjanya Komatineni wrote:
>
> On 4/30/20 10:06 AM, Sowjanya Komatineni wrote:
>>
>> On 4/30/20 9:29 AM, Sowjanya Komatineni wrote:
>>>
>>> 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.
>>
> To allow freeze b/w frames (but not in middle of a frame),
>
> for capture_start thread, probably we can do unconditional 
> try_to_freeze()
>
> for capture_finish thread, at end of capture done we can do 
> try_to_freeze() only when done list is empty
>
My understanding is buffer updates/release should not happen after 
frozen state. So we should let frame capture of outstanding buffer to 
finish before freezing in capture_finish thread.

But for capture_start thread we can unconditionally freeze before 
dequeuing next buffer for capture.

With this when both threads are in frozen state and no buffer 
updates/captures will happen after frozen state.

I think its not required to finish streaming of all frames completely to 
let threads to enter frozen state as streaming can be continuous as well.

>> Hi Dmitry,
>>
>> Will update in v12 to not allow freeze in middle of a frame capture.
>>
>> Can you please confirm on above if you agree to allow freeze to 
>> happen in b/w frame captures?
>>
>> Also as most feedback has been received from you by now, appreciate 
>> if you can provide all in this v11 if you have anything else so we 
>> will not have any new changes after v12.
>>
>> Thanks
>>
>> Sowjanya
>>