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: Tue, 7 Apr 2020 14:08:36 -0700 Message-ID: <84ad4e2d-6ac1-e1f4-1c55-5edaae850631@nvidia.com> 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> <760d071e-0cbc-b3eb-9231-fb9f9ecb44a6@nvidia.com> <9e317f65-8a02-3b15-cfec-8e0d8374130e@gmail.com> <97b35910-4c93-123a-43a0-eb14476ed0f3@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <97b35910-4c93-123a-43a0-eb14476ed0f3@nvidia.com> Content-Language: en-US Sender: linux-kernel-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 4:48 PM, Sowjanya Komatineni wrote: > > On 4/6/20 4:18 PM, Dmitry Osipenko wrote: >> External email: Use caution opening links or attachments >> >> >> 07.04.2020 01:07, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>> On 4/6/20 3:00 PM, Sowjanya Komatineni wrote: >>>> On 4/6/20 2:39 PM, Sowjanya Komatineni wrote: >>>>> On 4/6/20 2:15 PM, Sowjanya Komatineni wrote: >>>>>> On 4/6/20 2:11 PM, Dmitry Osipenko wrote: >>>>>>> External email: Use caution opening links or attachments >>>>>>> >>>>>>> >>>>>>> 07.04.2020 00:02, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1= =82: >>>>>>>>>>>>> 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=20 >>>>>>>>> >>>>>>>>> >>>>>>>> process is put to sleep until the condition evaluates to true or >>>>>>>> signal >>>>>>>> is received. >>>>>>>> >>>>>>>> condition is checked each time the waitqueue head is woken up. >>>>>>> This is a wrong assumption in accordance to the code. >>>> process is in sleep until the condition is evaluated and when >>>> condition is true wakeup still happens only when wake_up on waitqueue >>>> is called >>>> >>>> This is the reason for using this to prevent blocking while waiting >>>> for the buffers. >>> w.r.t capture list update, wakeup happens when wake_up on waitqueue is >>> called. >>> >>> wakeup also happens on kthread stop signal event. >>> >>>> >>>>>> when every buffer is available as long as we are in streaming, we >>>>>> should process it. >>>>>> >>>>>> So if wake up happens when list has buffer, it will be processed but >>>>>> at a time we limit processing 2 simultaneous buffer capture starts >>>>>> only. >>>>>> >>>>> Fixing typo. >>>>> >>>>> I meant when ever buffer is available as long as we are in streaming, >>>>> we should process it. >>>>> >>>>> So capture thread processes as long as buffers are available from >>>>> user space limiting 2 simultaneous trigger of captures and thread >>>>> will be in sleep when capture buffers list is empty or no stop thread >>>>> is signaled. >> IIUC, the waiting won't happen if more than 2 captures are queued and >> thread will be spinning until captures are processed. >> >> I think you need a semaphore with resource count =3D 2. > we hold on to issuing capture if more than 2 buffers are queued and it=20 > continues only after fifo has min 1 slot empty Just want to close on this part of feedback. Hope above explanation is=20 clear regarding triggering/issuing at max 2 frame capture to VI HW and=20 also regarding capture threads where they use wait_event_interruptible=20 to prevent blocking waiting for buffers to be available for captures. So no changes related to this part are needed in v7.