From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sowjanya Komatineni Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver Date: Mon, 6 Apr 2020 14:02:19 -0700 Message-ID: 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> <08cd31d5-e8b9-4d3a-fb0e-0e4462947d96@nvidia.com> <12a834ac-52b1-6dc0-7d3a-3e6a1fa85a2a@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <12a834ac-52b1-6dc0-7d3a-3e6a1fa85a2a@gmail.com> Content-Language: en-US Sender: linux-media-owner@vger.kernel.org To: Dmitry Osipenko , 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 List-Id: linux-tegra@vger.kernel.org On 4/6/20 1:56 PM, Dmitry Osipenko wrote: > External email: Use caution opening links or attachments > > > 06.04.2020 23:55, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> 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 =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>> 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 =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>>>> +static int chan_capture_kthread_start(void *data) >>>>>> +{ >>>>>> + struct tegra_vi_channel *chan =3D data; >>>>>> + struct tegra_channel_buffer *buf; >>>>>> + int err =3D 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 =3D chan->capture_reqs - >>>>>> chan->sequence; >>>>>> + /* >>>>>> + * Source is not streaming if error is non-zer= o. >>>>>> + * So, do not dequeue buffers on capture error >>>>>> or when >>>>>> + * syncpoint requests in FIFO are full. >>>>>> + */ >>>>>> + if (err || caps_inflight >=3D SYNCPT_FIFO_DEPT= H) >>>>>> + 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 process is put to sleep until the condition evaluates to true or signal=20 is received. condition is checked each time the waitqueue head is woken up. Also capture list may keep on getting updated with buffers from userspace. but at a time we only limit 2 frames as VI supports double buffering and=20 syncpt fifo's max depth is 2 Any more buffers waiting will be processing on subsequent iterations. So basically thread run time is depending on buffers getting queued from=20 userspace.