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From: Sowjanya Komatineni Message-ID: <89f0835c-d946-2288-b867-25f1ef1ae583@nvidia.com> Date: Mon, 4 May 2020 07:50:28 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [172.20.13.39] X-ClientProxiedBy: HQMAIL107.nvidia.com (172.20.187.13) To DRHQMAIL107.nvidia.com (10.27.9.16) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Content-Language: en-US DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1588603719; bh=8yGX7LmfP3dxzmPn9zc00N6IVAfMQdLzgvlsfYKzE20=; h=X-PGP-Universal:Subject:To:CC:References:From:Message-ID:Date: User-Agent:MIME-Version:In-Reply-To:X-Originating-IP: X-ClientProxiedBy:Content-Type:Content-Transfer-Encoding: Content-Language; b=NucxclL+MWs/EZiDmzt/9XMxunSA8BNQkYR+W5SQ9uK5Oo9RdoTzPXRXBOrRcM+X7 iVTSKXM0IPLI5aFvp1u1AolhMMOFociSVO62PqC54l03qPx4L35Y4l/ZWJWczLeNaw Clp6vjDkG0uKBQIrbX07gOcwNFk8YdrIiRHsSdyCm/rw7lpAI6scatQ4ELQOKoJ4r7 yn3npaYrkuNxUjYqNhT+IaDMWP1DTxCGJDo6BDZcEodbVtjOl0deCalsc8hq7wL+AU iAiTYzq9q1QUKhEehgwE/vNHSA8EBtubrAFMchPUnPU0T43eJ/Mb3WZOwjc3Vk4yVa VooggUMVe58fQ== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/4/20 5:18 AM, Hans Verkuil wrote: > On 03/05/2020 00:46, Sowjanya Komatineni wrote: >> On 5/2/20 1:48 PM, Dmitry Osipenko wrote: >>> 02.05.2020 19:55, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>> Also stop stream ioctl request happens during suspend where both threa= ds >>>> will be stopped properly. done thread stop happens only after finishin= g >>>> all outstanding buffers. >>> Do you mean that V4L core takes care of stopping the streami on suspend >>> and re-starting it on resume from suspend? >>> >>>> Stop stream request happens from streaming applications so even withou= t >>>> driver suspend/resume implementation currently, streaming will be >>>> stopped prior to system=C2=A0 suspend where both threads will be stopp= ed >>>> properly (after finishing out standing buffers) and will be resumed by >>>> application on system resume >>> All userspace is frozen on suspend. System suspension is transparent fo= r >>> userspace applications. I'm not sure what you're meaning here. >>> >>>> Also tested suspending while streaming with this unconditional freeze,= I >>>> don't see any issue as application stops stream where v4l_streamoff ge= ts >>>> executed during suspend and on resume streaming starts where >>>> v4l_streamon happens. >>>> >>>> So, I don't see any issue with existing implementation of unconditiona= l >>>> freeze. >>> I don't understand why freezing is needed at all if V4L core takes care >>> of stopping the stream on suspend, what is the point? If there is no >>> real point, then let's make threads non-freezable and done with that. >> video device fops unlocked_ioctl is set to video_ioctl2() in vi driver. >> >> video device fops unlocked_ioctl gets executed with stream off cmd >> during suspend and stream on cmd during resume which eventually calls >> v4l_streamoff and v4l_streamon during system suspend/resume. > That's news to me. The 'only' thing that suspend/resume needs to do is to > stop the HW DMA on suspend and to restart the HW DMA (and typically recon= figure > the whole HW video pipeline) on resume. Userspace doesn't do anything spe= cial. > > That's how e.g. a UVC webcam behaves when you close the lid of a laptop w= hile > it is streaming and open it again later. > > It can be hard to get this right, and I suspect many media drivers will f= ail > this test. when video device node path is kept opened during suspend, on suspend=20 entry looks like inode path is tried to closes and on resume opened=20 again causing v4l2 stream off/on thru v4l2 ioctl. Based on our testing even with downstream and user applications, we=20 always see video device node path close/open during suspend/resume which=20 does v4l2 stream off/on. >> My understanding to have freezable threads is during system suspend user >> space applications are frozen prior to kernel freeze and during suspend >> when opened video character device node gets closed these ioctl gets >> invoked and stream off during suspend and stream on during resume >> happens. So probably we still need to use freezable threads to sync with >> user space application when frozen before really entering suspend. >> >> Will wait for Thierry/Hans comment to correct if my above understanding >> is wrong and help clarify if we need freezable threads at all in this >> case... >> >> Note: I see other drivers using freezable threads for capture drivers. > Well, it's often a copy-and-paste without truly understanding what is > going on. You should not assume that the author knew what was happening. > > To be honest, I'm not an expert on this either. > > Looking at the tegra start/finish threads: they basically look at the > chan->capture and chan->done lists. Freezing the threads should not be > a problem as long as the actual suspend/resume doesn't mess with those > lists. If it does, then it may get tricky to prove that it is safe to > do suspend/resume (I think). > > An alternative is to stop and restart those threads when suspending or > resuming. Then those threads do not need to be 'freezable' and it might > be easier to validate the code. > > In any case, I do not want to postpone the merger of the upcoming v12 for > this. Changes can be done in later patches, if needed. > > Regards, > > Hans Thanks Hans. Buffers list don't get altered after frozen and during suspend/resume=20 till they are out of freeze. Will remove freezable threads and move on for v12. Will validate suspend/resume later after all sensor support. >> >> Assuming we use freezable threads, I was saying we don't need >> conditional try_to_freeze() like you pointed because even if finish >> thread freeze happens prior to frame capture initiated by start thread, >> vi hardware will still continue to update this single ongoing buffer and >> will finish max within 200ms and actually there is no direct processing >> of this done by finish thread itself except that it returns buffers back >> when done and in this case it returns back when unfreeze/wake up happens= . >> >> So, I don't see any issue of unconditional try_to_freeze() even with >> freezable threads. >> >> Thanks >> >> Sowjanya >> >>