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

[Sowjanya Komatineni]

On 7/17/20 8:01 AM, Dmitry Osipenko wrote:
> 17.07.2020 07:46, Sowjanya Komatineni ÐÐÑÐÑ:
> ...
> > Looks like sequence posted in TRM need to be updated clearly for proper
> > MIPI CAL start and wait.
> >
> > Correct steps should be like below
> >
> > 1. Set up CSI registers for use case such as number of lanes, virtual
> > channel, etc.
> > 2. Initialize and power up CSI CIL interface
> > 3. Program MIPI CAL bias pads, cal configs, cal control registers and
> > enable calibration start
> > 4. Power up camera through the I2C interface and start sensor streaming
> > through the I2C
> >
> > Note: All sensors might not leave pads in LP-11 state as sensor may be
> > power down when not in use.
> >
> > So start streaming prior to checking for calibration done status as
> > LP-11 -> HS transition happens during sensor stream and calibration
> > logic can apply results to pads and update done status,
> >
> > 5. Wait for done signal from calibration logic
> >
> > 6. perform frame capture thru VI
> > 7. Frame done, CSI goes back to stop state, LP11
> >
> > Will work internally to correct sequence in TRM ...
> Will be nice to have an updated TRM, thank you!
>
> Also, what about the auto-calibration? Isn't it needed to be enabled for
> CSI?
STARTCAL does one time calibration and with AUTOCAL calibration will be 
triggered periodically.

For pads PULLUP/PULLDN/TERM impedance calibration, we only need one-time 
calibration on pads power up.

We always use one time pads calibration for CSI.

> > In mipi driver will update as below to have mipi clk enabled till
> > calibration status check is done.
> >
> > Always tegra_mipi_wait() followes tegra_mipi_calibrate() in both DSI and
> > CSI. So below sequence should work good.
> >
> > tegra_mipi_calibrate()
> >
> > - clk_enable mipi cal
> > - program mipi cal registers (bias pads cfgs, mipi cal ctrl and trigger
> > calibration start)
> >
> > tegra_mipi_wait()
> > - read mipi cal status and wait for active and done bits
> > - clk_disable mipi cal
>
> Maybe then it should be better to rename the functions like this:
>
> tegra_mipi_calibrate() -> tegra_mipi_start_calibration()
> tegra_mipi_wait()      -> tegra_mipi_finish_calibration().
>
> and there also should be tegra_mipi_cancel_calibration().
>
>
> Example:
>
> 	tegra_mipi_start_calibration();
>
> 	ret = v4l2_subdev_call(subdev, video, s_stream, on);
> 	if (ret < 0) {
> 		tegra_mipi_cancel_calibration();
> 		goto err;
> 	}
>
> 	tegra_mipi_finish_calibration();