linux-kernel - Re: [RFC PATCH v3 16/18] gpu: host1x: mipi: Split tegra_mipi_calibrate and tegra_mipi

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Date:   Fri, 17 Jul 2020 02:47:52 +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 v3 16/18] gpu: host1x: mipi: Split
 tegra_mipi_calibrate and tegra_mipi_wait

17.07.2020 02:09, Sowjanya Komatineni пишет:
> 
> 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 пишет:
>>>>> 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-enabled
>>>> 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?