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Date: Thu, 30 Apr 2020 14:37:00 -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 2:26 PM, Sowjanya Komatineni wrote: > > On 4/30/20 2:17 PM, Dmitry Osipenko wrote: >> 30.04.2020 23:02, Sowjanya Komatineni пишет: >>> On 4/30/20 12:53 PM, Sowjanya Komatineni wrote: >>>> On 4/30/20 12:46 PM, Sowjanya Komatineni wrote: >>>>> On 4/30/20 12:33 PM, Dmitry Osipenko wrote: >>>>>> 30.04.2020 22:09, Sowjanya Komatineni пишет: >>>>>>> On 4/30/20 11:18 AM, Sowjanya Komatineni wrote: >>>>>>>> On 4/30/20 10:06 AM, Sowjanya Komatineni wrote: >>>>>>>>> On 4/30/20 9:29 AM, Sowjanya Komatineni wrote: >>>>>>>>>> On 4/30/20 9:04 AM, Sowjanya Komatineni wrote: >>>>>>>>>>> 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. >>>>>>>>>>> >>>>>>>>>> Also if we add check for both lists empty, freeze is not >>>>>>>>>> allowed as >>>>>>>>>> long as streaming is going on and in case of continuous >>>>>>>>>> streaming >>>>>>>>>> freeze will never happen. >>>>>>>> To allow freeze b/w frames (but not in middle of a frame), >>>>>>>> >>>>>>>> for capture_start thread, probably we can do unconditional >>>>>>>> try_to_freeze() >>>>>> Is it possible to use wait_event_freezable()? >>>>>> >>>>>> https://www.kernel.org/doc/Documentation/power/freezing-of-tasks.txt >>>>>> >>>>>> Will the wait_event_interruptible() be woken up when system freezes? >>>>> Based on wait_event_freezable implementation, looks like it similar >>>>> to wait_event_interruptible + try_to_free() as it does >>>>> freezable_schedule unlike schedule with wait_event_interruptible. >>>>> >>>>> So using this for capture_start may be ok to allow freeze before >>>>> start of frame. But can't use for capture_finish as this is same as >>>>> wait_event_interruptible followed by unconditional try_to_freeze. >>>>> >>>>>>>> for capture_finish thread, at end of capture done we can do >>>>>>>> try_to_freeze() only when done list is empty >>>>>> This doesn't prevent situation where the done-list is empty and the >>>>>> "finish" thread freezes, in the same time the "start" thread >>>>>> issues new >>>>>> capture and then freezes too. >>>>>> >>>>>> 1. "start" thread issues capture >>>>>> >>>>>> 2. "finish" thread wakes and waits for the capture to complete >>>>>> >>>>>> 3. "start" thread begins another capture, waits for FRAME_START >>>>>> >>>>>> 4. system freezing activates >>>>>> >>>>>> 5. "finish" thread completes the capture and freezes because >>>>>> done-list >>>>>> is empty >>>>>> >>>>>> 6. "start" thread gets FRAME_START, issues another capture and >>>>>> freezes >>>>> This will not happen as we allow double buffering done list will not >>>>> be empty till stream stop happens >>>>> >>>>> There will always be 1 outstanding frame in done list >>>> Correction, there will always be 1 outstanding buffer except beginning >>>> during beginning of stream. >>>> >>>> Except during beginning frames, done list will not be empty for all >>>> subsequent streaming process >>> Also to be clear, hardware sees next frame start event prior to >>> previous >>> frame mw_ack event as mw_ack event happens after frame end. So once >>> initial buffer got queued to done list to finish processes, while >>> waiting for mw_ack next frame start happens and pushes next buffer to >>> done list. >> What about this variant: >> >> 1. "start" thread wakes up to start capture >> >> 2. system freezing activates >> >> 3. "finish" thread wakes up and freezes > > finish thread will wake up only when done list is not > empty/kthread_stop/wake even from capture start thread. > > Also when I said will allow try_to_free when done list is empty I > meant to have this at end of capture_done() in finish thread > >> >> 4. "start" thread issues capture and freezes >> >> And again, I assume that system's freezing should wake >> wait_event_interruptible(), otherwise it won't be possible to freeze >> idling threads at all and freezing should fail (IIUC). > > Based on kernel doc on freezing, looks like when we mark thread as > freezable, freeze state happens when we explicitly call try_to_freeze. > > I don't think its other way where freeze causes > wait_event_interruptible to wake up. > >> And in this case synchronization between start/finish threads should be >> needed in regards to freezing. > > Was thinking to have counter to track outstanding frame w.r.t single > shot issue b/w start and finish and allow to freeze only when no > outstanding frames in process. > > This will make sure freeze will not happen when any buffers are in > progress > >> Note that this could be a wrong assumption, I'm not closely familiar >> with how freezer works. kthread_start can unconditionally allow try_to_freeze before start of frame capture We can compute captures inflight w.r.t single shot issued during capture start and finished frames by kthread_finish and allow kthread_finish to freeze only when captures inflight is 0. This allows freeze to happen b/w frames but not in middle of frame
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