Re: [RFC PATCH v3 16/18] gpu: host1x: mipi: Split tegra_mipi_calibrate and tegra_mipi_wait

[Sowjanya Komatineni]

On 7/16/20 4:47 PM, Dmitry Osipenko wrote:
> 17.07.2020 02:09, Sowjanya Komatineni ÐÐÑÐÑ:
> > 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 ÐÐÑÐÑ:
> > > > > > 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?

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

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