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Subject: Re: [PATCH v8 08/10] gpu: host1x: mipi: Keep MIPI clock enabled till
 calibration is done
From:   Sowjanya Komatineni <skomatineni@nvidia.com>
To:     Dmitry Osipenko <digetx@gmail.com>,
        Thierry Reding <thierry.reding@gmail.com>
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On 8/6/20 11:44 AM, Sowjanya Komatineni wrote:
>
> 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=20
>>>>> active to
>>>>> 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=20
>>> 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=20
> used during calibrate is device specific lock.
> So, it will not prevent other devices to hold till on going=20
> calibration is done unless we add wait for active bit before=20
> 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=20
> devices it will trigger start but MIPI calibration logic ignore if=20
> previous calibration is still in progress.
>
> Need to serialize calibration start requests from different devices=20
> based on ACTIVE bit.

Sorry confused. MIPI driver is using common lock from tegra_mipi for all=20
tegra_mipi_device

So should be ok as only one device start_calibration can happen at a time.

But its still good to check ACTIVE is cleared and to report as error if=20
not as ACTIVE will be cleared once set of pads enabled for this calibration=
.

Eg: CSI port can be 4 lane and all 4 pads gets enabled at same time and=20
with this ACTIVE should still be verified to be 0 to make sure all pads=20
calibration is done

>
>>>> 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=20
>>> 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#L=
350=20
>>
>>
>> Although looks like auto-calibration isn't supported by the current=20
>> driver.
>
> Yes we don't use auto-calibration.
>
> Only common bit here is MIPI_CAL_CTRL start. All others are pad=20
> specific currently.
>