linux-kernel - Re: [RFC PATCH v5 12/14] gpu: host1x: mipi: Keep MIPI clock enabled till calibration is done

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Date:   Thu, 30 Jul 2020 02:42:14 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com, frankc@...dia.com,
        hverkuil@...all.nl, sakari.ailus@....fi, robh+dt@...nel.org,
        helen.koike@...labora.com
Cc:     sboyd@...nel.org, gregkh@...uxfoundation.org,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org
Subject: Re: [RFC PATCH v5 12/14] gpu: host1x: mipi: Keep MIPI clock enabled
 till calibration is done

29.07.2020 20:55, Sowjanya Komatineni пишет:
> 
> On 7/29/20 10:08 AM, Dmitry Osipenko wrote:
>> 28.07.2020 19:04, Sowjanya Komatineni пишет:
>> ...
>>>>> +void tegra_mipi_cancel_calibration(struct tegra_mipi_device *device)
>>>>> +{
>>>> Doesn't MIPI_CAL need to be reset here?
>>> No need to reset MIPI CAL
>> Could you please explain why. There is a calibration state-machine that
>> apparently needs to be returned into initial state, does it return by
>> itself?
>>
>> TRM says that MIPI block needs to be reset before of starting
>> calibration process. The reset is completely missing in the driver, I
>> assume it needs to be corrected with another patch.
> 
> TRM documented incorrectly. There is no need to reset MIPI_CAL.
> 
> MIPI CAL is FSM and it does not hang and done bit is to indicate if
> results are applied to pads or not.
> 
> If we don't see done bit set meaning, MIPI CAL did not see LP-11 and
> results are not applied to pads.

But how to stop calibration from triggering on LP-11 once it has been
enabled? The reset should be needed since there is no other way to reset
the calibration state.

> Also while multiple streams can happen in parallel and we can't reset
> MIPI CAL as other CSI channel streams (using other pads) may also be
> going thru calibration process in parallel depending and also DSI pads
> also are calibrated thru same MIPI CAL controller.

Perhaps this should be the case for a shared reset control API usage.