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

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Date:   Thu, 30 Apr 2020 11:18:09 -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 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

> 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
>