Re: [RFC PATCH v5 12/14] gpu: host1x: mipi: Keep MIPI clock enabled till calibration is done

[Sowjanya Komatineni]

On 7/29/20 4:42 PM, Dmitry Osipenko wrote:
> 29.07.2020 20:55, Sowjanya Komatineni ÐÐÑÐÑ:
> > On 7/29/20 10:08 AM, Dmitry Osipenko wrote:
> > > 28.07.2020 19:04, Sowjanya Komatineni ÐÐÑÐÑ:
> > > ...
> > > > > > +void tegra_mipi_cancel_calibration(struct tegra_mipi_device *device)
> > > > > > +{
> > > > > Doesn't MIPI_CAL need to be reset here?
> > > > No need to reset MIPI CAL
> > > Could you please explain why. There is a calibration state-machine that
> > > apparently needs to be returned into initial state, does it return by
> > > itself?
> > >
> > > TRM says that MIPI block needs to be reset before of starting
> > > calibration process. The reset is completely missing in the driver, I
> > > assume it needs to be corrected with another patch.
> > TRM documented incorrectly. There is no need to reset MIPI_CAL.
> >
> > MIPI CAL is FSM and it does not hang and done bit is to indicate if
> > results are applied to pads or not.
> >
> > If we don't see done bit set meaning, MIPI CAL did not see LP-11 and
> > results are not applied to pads.
> But how to stop calibration from triggering on LP-11 once it has been
> enabled? The reset should be needed since there is no other way to reset
> the calibration state.

Its a finite state machine that goes thru fixed steps of sequence codes 
internally and holds results in registers.

When it sees LP-11 results are applied to pads.

If it does not see LP-11, next start will again trigger calibrating with 
finite sequence codes.

As per HW designers, we don't have to do any reverts when done bit is 
not set.

> > Also while multiple streams can happen in parallel and we can't reset
> > MIPI CAL as other CSI channel streams (using other pads) may also be
> > going thru calibration process in parallel depending and also DSI pads
> > also are calibrated thru same MIPI CAL controller.
> Perhaps this should be the case for a shared reset control API usage.