linux-kernel - Re: [PATCH v8 08/10] gpu: host1x: mipi: Keep MIPI clock enabled till calibration is done

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Date:   Thu, 6 Aug 2020 21:18:34 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     jonathanh@...dia.com, frankc@...dia.com, hverkuil@...all.nl,
        sakari.ailus@....fi, robh+dt@...nel.org, helen.koike@...labora.com,
        gregkh@...uxfoundation.org, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 08/10] gpu: host1x: mipi: Keep MIPI clock enabled till
 calibration is done

06.08.2020 21:07, Sowjanya Komatineni пишет:
> 
> On 8/6/20 11:01 AM, Dmitry Osipenko wrote:
>> 06.08.2020 20:52, Sowjanya Komatineni пишет:
>> ...
>>> Right mutex_unlock should happen at end of finish_calibration.
>>>
>>> With keeping mutex locked in start, we dont have to check for 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 = 0 and DONE = 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.

>>> - mutex_unlock()
>> 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#L350

Although looks like auto-calibration isn't supported by the current driver.