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

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Message-ID: <a6604949-5675-50ae-160d-d1a26f0a9c0b@gmail.com>
Date:   Thu, 30 Jul 2020 03:31:20 +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

30.07.2020 02:54, Sowjanya Komatineni пишет:
> 
> On 7/29/20 4:42 PM, Dmitry Osipenko wrote:
>> 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.
> 
> Its a finite state machine that goes thru fixed steps of sequence codes
> internally and holds results in registers.
> 
> When it sees LP-11 results are applied to pads.
> 
> If it does not see LP-11, next start will again trigger calibrating with
> finite sequence codes.
> 
> As per HW designers, we don't have to do any reverts when done bit is
> not set.

Alright, then should be good if HW can't stuck.

Reviewed-by: Dmitry Osipenko <digetx@...il.com>