Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver
To:     Sowjanya Komatineni <skomatineni@nvidia.com>,
        thierry.reding@gmail.com, jonathanh@nvidia.com, frankc@nvidia.com,
        hverkuil@xs4all.nl, sakari.ailus@iki.fi, helen.koike@collabora.com
Cc:     sboyd@kernel.org, linux-media@vger.kernel.org,
        devicetree@vger.kernel.org, linux-clk@vger.kernel.org,
        linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1585963507-12610-1-git-send-email-skomatineni@nvidia.com>
 <1585963507-12610-7-git-send-email-skomatineni@nvidia.com>
 <200bb96e-2d07-764f-9e14-55538dc742fd@gmail.com>
 <23bfab09-b464-6e51-9843-06d13000e9b9@nvidia.com>
 <be77b0ef-d605-8357-4180-f40b2886d07a@gmail.com>
 <08cd31d5-e8b9-4d3a-fb0e-0e4462947d96@nvidia.com>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <12a834ac-52b1-6dc0-7d3a-3e6a1fa85a2a@gmail.com>
Date:   Mon, 6 Apr 2020 23:56:28 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.5.0
MIME-Version: 1.0
In-Reply-To: <08cd31d5-e8b9-4d3a-fb0e-0e4462947d96@nvidia.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

06.04.2020 23:55, Sowjanya Komatineni пишет:
> 
> On 4/6/20 1:53 PM, Dmitry Osipenko wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> 06.04.2020 23:50, Sowjanya Komatineni пишет:
>>> On 4/6/20 1:45 PM, Dmitry Osipenko wrote:
>>>> External email: Use caution opening links or attachments
>>>>
>>>>
>>>> 04.04.2020 04:25, 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;
>>>>> +     int caps_inflight;
>>>>> +
>>>>> +     set_freezable();
>>>>> +
>>>>> +     while (1) {
>>>>> +             try_to_freeze();
>>>>> +
>>>>> +             wait_event_interruptible(chan->start_wait,
>>>>> +                                      !list_empty(&chan->capture) ||
>>>>> +                                      kthread_should_stop());
>>>>> +             /*
>>>>> +              * Frame start and MW_ACK_DONE syncpoint condition
>>>>> FIFOs are
>>>>> +              * of max depth 2. So make sure max 2 capture
>>>>> requests are
>>>>> +              * in process by the hardware at a time.
>>>>> +              */
>>>>> +             while (!(kthread_should_stop() ||
>>>>> list_empty(&chan->capture))) {
>>>>> +                     caps_inflight = chan->capture_reqs -
>>>>> chan->sequence;
>>>>> +                     /*
>>>>> +                      * Source is not streaming if error is non-zero.
>>>>> +                      * So, do not dequeue buffers on capture error
>>>>> or when
>>>>> +                      * syncpoint requests in FIFO are full.
>>>>> +                      */
>>>>> +                     if (err || caps_inflight >= SYNCPT_FIFO_DEPTH)
>>>>> +                             break;
>>>> Am I understanding correctly that this thread will take 100% CPU,
>>>> spinning here, if more than 2 frame-captures queued?
>>> on more than 2 frames captures, it breaks thread and on next wakeup it
>>> continues
>> The wait_event() won't wait if condition is true.
> condition is checked when waitqueue is woken up

https://elixir.bootlin.com/linux/v5.6.2/source/include/linux/wait.h#L462