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 19:10:51 +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 18:59, Sowjanya Komatineni пишет:
...
>>> Confirmed from HW designer, calibration FSM to finish takes worst case
>>> 72uS so by the time it gets to sensor stream it will be done its
>>> sequence and will be waiting for DONE bit.
>>>
>>> So disabling MIPI CAL clock on sensor stream fails is safe.
>>
>> 72us is quite a lot of time, what will happen if LP-11 happens before
>> FSM finished calibration?
>>
>> Maybe the finish_calibration() needs to split into two parts:
>>
>>   1. wait for CAL_STATUS_ACTIVE before enabling sensor
>>   2. wait for CAL_STATUS_DONE after enabling sensor
> 
> I don't think we need to split for active and done. Active will be 1 as
> long as other pads are in calibration as well.
> 
> We cant use active status check for specific pads under calibration.
> This is common bit for all pads.

Does hardware have a single FSM block shared by all pads or there is FSM
per group of pads?

> Unfortunately HW don't have separate status indicating when sequence is
> done to indicate its waiting for LP11.
> 
> 
> To avoid all this, will remove cancel_calibration() totally and use same
> finish calibration even in case of stream failure then.
> 

What about to add 72us delay to the end of start_calibration() in order
to ensure that FSM is finished before LP-11?