linux-kernel - Re: [PATCH v9 08/10] gpu: host1x: mipi: Keep MIPI clock enabled and mutex locked till calibration done

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Date:   Fri, 7 Aug 2020 07:08:08 +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:     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 v9 08/10] gpu: host1x: mipi: Keep MIPI clock enabled and
 mutex locked till calibration done

07.08.2020 07:06, Sowjanya Komatineni пишет:
> 
> On 8/6/20 9:05 PM, Sowjanya Komatineni wrote:
>>
>> On 8/6/20 9:01 PM, Dmitry Osipenko wrote:
>>> 07.08.2020 06:18, Sowjanya Komatineni пишет:
>>>> On 8/6/20 8:14 PM, Sowjanya Komatineni wrote:
>>>>> On 8/6/20 8:10 PM, Sowjanya Komatineni wrote:
>>>>>> On 8/6/20 7:31 PM, Dmitry Osipenko wrote:
>>>>>>> 06.08.2020 22:01, Sowjanya Komatineni пишет:
>>>>>>> ...
>>>>>>>> +int tegra_mipi_start_calibration(struct tegra_mipi_device *device)
>>>>>>>>    {
>>>>>>>>        const struct tegra_mipi_soc *soc = device->mipi->soc;
>>>>>>>>        unsigned int i;
>>>>>>>> @@ -381,12 +375,16 @@ int tegra_mipi_calibrate(struct
>>>>>>>> tegra_mipi_device *device)
>>>>>>>>        value |= MIPI_CAL_CTRL_START;
>>>>>>>>        tegra_mipi_writel(device->mipi, value, MIPI_CAL_CTRL);
>>>>>>>>    -    mutex_unlock(&device->mipi->lock);
>>>>>>>> -    clk_disable(device->mipi->clk);
>>>>>>>> +    /*
>>>>>>>> +     * Wait for min 72uS to let calibration logic finish
>>>>>>>> calibration
>>>>>>>> +     * sequence codes before waiting for pads idle state to
>>>>>>>> apply the
>>>>>>>> +     * results.
>>>>>>>> +     */
>>>>>>>> +    usleep_range(75, 80);
>>>>>>> Could you please explain why the ACTIVE bit can't be polled
>>>>>>> instead of
>>>>>>> using the fixed delay? Doesn't ACTIVE bit represents the state of
>>>>>>> the
>>>>>>> busy FSM?
>>>>>> Based on internal discussion, ACTIVE bit gets cleared when all
>>>>>> enabled pads calibration is done (same time as when DONE set to 1).
>>>>>>
>>>>>> Will request HW designer to look into design and confirm exactly when
>>>>>> ACTIVE bit gets cleared.
>>>>>>
>>>>>> Will get back on this.
>>>>>>
>>>>> Verified with HW designer. above is correct. ACTIVE bit update happens
>>>>> same time as DONE bit.
>>>>>
>>>>> Active = !(DONE)
>>>>>
>>>>> In case of calibration logic waiting for LP-11 where done bit does not
>>>>> get set, ACTIVE will still be 1 and on next start trigger new
>>>>> calibration will start
>>>>>
>>>> Based on internal design check from designer, as long as its in waiting
>>>> for LP-11 stage, next calibration request can be triggered again but
>>>> ACTIVE bit we will see it at 1. So we should check for DONE bits to
>>>> confirm if calibration is done or not.
>>>>
>>>> To start next calibration, it can take effect as long as its in wait
>>>> for
>>>> LP-11 mode.
>>> I meant the start_calibration() will poll the ACTIVE bit (calibration
>>> busy), while the finish_calibration() will poll the DONE bit
>>> (calibration applied).
>>
>> ACTIVE bit can be 1 when previous calibration process does not see LP-11.
>>
>> So there is no need to use ACTIVE bit during start of calibration.
>>
>> At HW level, both ACTIVE and DONE bits get set at same time.
>>
>> So waiting for ACTIVE to be 0 during start calibration instead of
>> *75uS will not work as ACTIVE bit will not become 0 after calibration
>> sequence codes and it will get updated along with DONE bits only after
>> applying results to pads which happens after seeing LP-11 on pads.
>>
> *typo fixed

I see now, thank you.