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

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Message-ID: <b14b9dc5-7ac9-7735-d98d-eebc7e151cba@nvidia.com>
Date:   Thu, 30 Apr 2020 09:04:40 -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 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.