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Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver
To:     Dmitry Osipenko <digetx@gmail.com>, <thierry.reding@gmail.com>,
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From:   Sowjanya Komatineni <skomatineni@nvidia.com>
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On 4/6/20 9:29 AM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 06.04.2020 19:12, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>> On 4/6/20 9:05 AM, Dmitry Osipenko wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> 06.04.2020 18:35, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>> ...
>>>>>> +     /* wait for syncpt counter to reach frame start event
>>>>>> threshold */
>>>>>> +     err =3D host1x_syncpt_wait(chan->frame_start_sp, thresh,
>>>>>> +                              TEGRA_VI_SYNCPT_WAIT_TIMEOUT, &value)=
;
>>>>>> +     if (err) {
>>>>>> +             dev_err(&chan->video.dev,
>>>>>> +                     "frame start syncpt timeout: %d\n", err);
>>>>>> +             /* increment syncpoint counter for timedout events */
>>>>>> +             host1x_syncpt_incr(chan->frame_start_sp);
>>>>> Why incrementing is done while hardware is still active?
>>>>>
>>>>> The sync point's state needs to be completely reset after resetting
>>>>> hardware. But I don't think that the current upstream host1x driver
>>>>> supports doing that, it's one of the known-long-standing problems of
>>>>> the
>>>>> host1x driver.
>>>>>
>>>>> At least the sp->max_val incrementing should be done based on the
>>>>> actual
>>>>> syncpoint value and this should be done after resetting hardware.
>>>> upstream host1x driver don't have API to reset or to equalize max valu=
e
>>>> with min/load value.
>>>>
>>>> So to synchronize missed event, incrementing HW syncpt counter.
>>>>
>>>> This should not impact as we increment this in case of missed events
>>>> only.
>>> It's wrong to touch sync point while hardware is active and it's active
>>> until being reset.
>>>
>>> You should re-check the timeout after hw resetting and manually put the
>>> syncpoint counter back into sync only if needed.
>> There is possibility of timeout to happen any time even during the
>> capture also and is not related to hw reset.
>>
>> Manual synchronization is needed when timeout of any frame events happen
>> otherwise all subsequence frames will timeout due to mismatch in event
>> counters.
> My point is that hardware is stopped only after being reset, until then
> you should assume that sync point could be incremented by HW at any time.
>
> And if this happens that HW increments sync point after the timeout,
> then the sync point counter should become out-of-sync in yours case,
> IIUC. Because host1x_syncpt_incr() doesn't update the cached counter.

We wait for enough time based on frame rate for syncpt increment to=20
happen and if it doesn't happen by then definitely its missed event and=20
we increment HW syncpoint for this timed event.

cached value gets updated during syncpt wait for subsequent event.

syncpt increment happens for all subsequent frame events during video=20
capture.