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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 9:05 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 th=
e
>>> host1x driver.
>>>
>>> At least the sp->max_val incrementing should be done based on the actua=
l
>>> syncpoint value and this should be done after resetting hardware.
>> upstream host1x driver don't have API to reset or to equalize max value
>> 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 onl=
y.
> 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=20
capture also and is not related to hw reset.

Manual synchronization is needed when timeout of any frame events happen=20
otherwise all subsequence frames will timeout due to mismatch in event=20
counters.