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

[Sowjanya Komatineni <skomatineni@nvidia.com>]

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