Re: [PATCH v8 08/10] gpu: host1x: mipi: Keep MIPI clock enabled till calibration is done

[Sowjanya Komatineni]

On 8/6/20 11:44 AM, Sowjanya Komatineni wrote:
> On 8/6/20 11:18 AM, Dmitry Osipenko wrote:
> > 06.08.2020 21:07, Sowjanya Komatineni пишет:
> > > On 8/6/20 11:01 AM, Dmitry Osipenko wrote:
> > > > 06.08.2020 20:52, Sowjanya Komatineni пишет:
> > > > ...
> > > > > Right mutex_unlock should happen at end of finish_calibration.
> > > > >
> > > > > With keeping mutex locked in start, we dont have to check for 
> > > > > active to
> > > > > be 0 to issue start as mutex will keep it locked and other pads
> > > > > calibration can only go thru when current one is done.
> > > > >
> > > > > So instead of below sequence, its simpler to do this way?
> > > > >
> > > > > start_calibration()
> > > > >
> > > > > - mutex_lock
> > > > >
> > > > > - wait for 72uS after start
> > > > >
> > > > > finish_calibration()
> > > > >
> > > > > - keep check for ACTIVE = 0 and DONE = 1
> > > > I think only the DONE bits which correspond to the mipi_device->pads
> > > > bitmask should be awaited.
> > > As next START can't be triggered when auto cal is ACTIVE, we should 
> > > keep
> > > this in finish.
> > >
> > > As we do mutex_unlock only at end of finish, other pads calibrations
> > > dont go thru till the one in process is finished.
> > >
> > > So in this case ACTIVE applies to current selected pads that are under
> > > calibration.
> > Should be better to check only the relevant bits in order to catch bugs,
> > otherwise you may get a DONE status from the irrelevant pads.
> tegra_mipi_device is separate for DSI and CSI channels. mutex lock 
> used during calibrate is device specific lock.
> So, it will not prevent other devices to hold till on going 
> calibration is done unless we add wait for active bit before 
> triggering start.
>
> Currently we wait for active bit at end during calibration done check 
> after start trigger. But when other devices go thru calibration in 
> parallel as lock is device specific and not common lock for all 
> devices it will trigger start but MIPI calibration logic ignore if 
> previous calibration is still in progress.
>
> Need to serialize calibration start requests from different devices 
> based on ACTIVE bit.

Sorry confused. MIPI driver is using common lock from tegra_mipi for all 
tegra_mipi_device

So should be ok as only one device start_calibration can happen at a time.

But its still good to check ACTIVE is cleared and to report as error if 
not as ACTIVE will be cleared once set of pads enabled for this calibration.

Eg: CSI port can be 4 lane and all 4 pads gets enabled at same time and 
with this ACTIVE should still be verified to be 0 to make sure all pads 
calibration is done

> > > > Perhaps the start_calibration() also needs to be changed to not touch
> > > > the MIPI_CAL_CONFIG bits of the unrelated pads?
> > > Driver already takes care of programming corresponding pads config 
> > > only.
> > It writes 0 to the config of the unrelated pads, which probably isn't
> > nice if some pads use periodic auto-calibration.
> >
> > https://elixir.bootlin.com/linux/v5.8/source/drivers/gpu/host1x/mipi.c#L350 
> >
> >
> > Although looks like auto-calibration isn't supported by the current 
> > driver.
>
> Yes we don't use auto-calibration.
>
> Only common bit here is MIPI_CAL_CTRL start. All others are pad 
> specific currently.