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Subject: Re: [RFC PATCH v3 16/18] gpu: host1x: mipi: Split
 tegra_mipi_calibrate and tegra_mipi_wait
To:     Dmitry Osipenko <digetx@gmail.com>, <thierry.reding@gmail.com>,
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From:   Sowjanya Komatineni <skomatineni@nvidia.com>
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Date:   Thu, 16 Jul 2020 17:16:36 -0700
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On 7/16/20 4:47 PM, Dmitry Osipenko wrote:
> 17.07.2020 02:09, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>> On 7/16/20 4:06 PM, Sowjanya Komatineni wrote:
>>> On 7/16/20 4:01 PM, Dmitry Osipenko wrote:
>>>> 17.07.2020 01:49, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>>>>> What keeps MIPI clock enabled after completion of the
>>>>>> tegra_mipi_calibrate() invocation?
>>>>> MIPI clock is disabled at end of tegra_mipi_calibrate and is re-enabl=
ed
>>>>> during tegra_mipi_wait.
>>>>>
>>>>> I think I should fix this to keep the clock enabled till calibration
>>>>> results are latched.
>>>>>
>>>>> All consumers of tegra_mipi_calibrate() will call tegra_mipi_wait().
>>>>>
>>>>> So will remove clk_disable mipi clk at end of tegra_mipi_calibrate()
>>>>> and
>>>>> clk_enable mipi_clk at beginning of tegra_mipi_wait()
>>>> Isn't it possible to perform the calibration after enabling CSI and
>>>> before of starting the sensor streaming?
>>> Currently this is what I am doing. Triggering calibration start during
>>> CSI receiver being ready and then sensor streaming will happen where
>>> internal MIPI CAL detects for LP -> HS transition and applies results
>>> to pads. So checking for calibration results after sensor stream is
>>> enabled
>> 1. Calling tegra_mipi_calibrate() during CSI streaming where CSI pads
>> are enabled and receiver is kept ready
>>
>> 2. Start Sensor stream
>>
>> 3. Calling tegra_mipi_wait() to check for MIPI Cal status.
>>
>> So as mipi cal clk need to be kept enabled till 3rd step, we can enable
>> clock during tegra_mipi_calibrate() and leave it enabled and disable it
>> in tegra_mipi_wait after status check.
>  From TRM:
>
> The following sequence is recommended for capturing a single frame:
>
> 1. Set up CSI registers for use case such as number of lanes, virtual
> channel, etc.
> 2. Initialize and power up CSI interface
> 3. Wait for initialization time or done signal from calibration logic
> 4. Power up camera through the I2C interface
> 5. All CSI data and clock lanes are in stop state, LP11
> 6. Initiate frame capture through the I2C
> 7. Frame done, CSI goes back to stop state, LP11
>
> Hence, is it really necessary to perform the manual calibration?

done signal from calibration logic will happen only when it sees LP to=20
HS transition as thats when calibration results are applied to pads and=20
then done signal is set.

Also MIPI Pads calibration need to be done on every power off/on. So=20
need to do calibration and trigger it along with CSI receiver=20
programming to keep it ready and then need to check/wait for status only=20
after sensor stream happens as thats where LP->HS transition happen.