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Subject: Re: [PATCH v8 08/10] gpu: host1x: mipi: Keep MIPI clock enabled till
 calibration is done
To:     Dmitry Osipenko <digetx@gmail.com>,
        Thierry Reding <thierry.reding@gmail.com>
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From:   Sowjanya Komatineni <skomatineni@nvidia.com>
Message-ID: <50aa439e-a572-ce77-9d06-e060304b9bd4@nvidia.com>
Date:   Thu, 6 Aug 2020 11:44:04 -0700
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On 8/6/20 11:18 AM, Dmitry Osipenko wrote:
> 06.08.2020 21:07, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>> On 8/6/20 11:01 AM, Dmitry Osipenko wrote:
>>> 06.08.2020 20:52, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>> ...
>>>> Right mutex_unlock should happen at end of finish_calibration.
>>>>
>>>> With keeping mutex locked in start, we dont have to check for active t=
o
>>>> be 0 to issue start as mutex will keep it locked and other pads
>>>> calibration can only go thru when current one is done.
>>>>
>>>> So instead of below sequence, its simpler to do this way?
>>>>
>>>> start_calibration()
>>>>
>>>> - mutex_lock
>>>>
>>>> - wait for 72uS after start
>>>>
>>>> finish_calibration()
>>>>
>>>> - keep check for ACTIVE =3D 0 and DONE =3D 1
>>> I think only the DONE bits which correspond to the mipi_device->pads
>>> bitmask should be awaited.
>> As next START can't be triggered when auto cal is ACTIVE, we should keep
>> this in finish.
>>
>> As we do mutex_unlock only at end of finish, other pads calibrations
>> dont go thru till the one in process is finished.
>>
>> So in this case ACTIVE applies to current selected pads that are under
>> calibration.
> Should be better to check only the relevant bits in order to catch bugs,
> otherwise you may get a DONE status from the irrelevant pads.
tegra_mipi_device is separate for DSI and CSI channels. mutex lock used=20
during calibrate is device specific lock.
So, it will not prevent other devices to hold till on going calibration=20
is done unless we add wait for active bit before triggering start.

Currently we wait for active bit at end during calibration done check=20
after start trigger. But when other devices go thru calibration in=20
parallel as lock is device specific and not common lock for all devices=20
it will trigger start but MIPI calibration logic ignore if previous=20
calibration is still in progress.

Need to serialize calibration start requests from different devices=20
based on ACTIVE bit.

>>> Perhaps the start_calibration() also needs to be changed to not touch
>>> the MIPI_CAL_CONFIG bits of the unrelated pads?
>> Driver already takes care of programming corresponding pads config only.
> It writes 0 to the config of the unrelated pads, which probably isn't
> nice if some pads use periodic auto-calibration.
>
> https://elixir.bootlin.com/linux/v5.8/source/drivers/gpu/host1x/mipi.c#L3=
50
>
> Although looks like auto-calibration isn't supported by the current drive=
r.

Yes we don't use auto-calibration.

Only common bit here is MIPI_CAL_CTRL start. All others are pad specific=20
currently.