[libcamera-devel] [PATCH v2 12/14] ipa: ipu3: Cache line duration at configure call

[Kieran Bingham]

Quoting Kieran Bingham (2021-11-10 23:10:49)
> Quoting Jean-Michel Hautbois (2021-11-10 19:58:59)
> > We use the line duration several times in the IPAIPU3. Instead of
> > recalculating it each time, cache the value as a utils::Duration. When
> > the value is needed in double, call the intern count() function to get
> > it.
> 
> caching it I like ... using the internal count() ... sounds scary...
> 
> Oh ... in fact, it does look like the 'correct' way to do this.
> But I think that's a limitation on our implementation of
> utils::Duration.
> 
> I think we can do:
>         maxShutterSpeed = maxExposure * lineDuration.get<std::nano>();
> 
> But that essentially just casts a std::nano to a std::nano and then
> calls .count() on it ... so that's a bit redundant compared to what
> you're already doing...
> 
> Perhaps we should have our Duration class implement a default .get()
> which always returns nanoseconds.... (and simply calls .count() or an
> explicit operator double() ... ?)
> 
> Anyway, that isn't a fault of this patch as far as I can tell - so lets
> consider that on top.
> 
> If you prefer the explicit named cast with .get<std::nano>() I think
> it's ok to use that as the compiler will probably optimise it ... but
> either way is up to you I think...
> 
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

Hrm... perhaps except for one more thing to check first ...


> 
> > Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> > ---
> >  src/ipa/ipu3/ipu3.cpp | 17 +++++++++--------
> >  1 file changed, 9 insertions(+), 8 deletions(-)
> > 
> > diff --git a/src/ipa/ipu3/ipu3.cpp b/src/ipa/ipu3/ipu3.cpp
> > index eb8c0dc4..68a97e8e 100644
> > --- a/src/ipa/ipu3/ipu3.cpp
> > +++ b/src/ipa/ipu3/ipu3.cpp
> > @@ -174,6 +174,8 @@ private:
> >         uint32_t minGain_;
> >         uint32_t maxGain_;
> >  
> > +       utils::Duration lineDuration_;
> > +
> >         /* Interface to the Camera Helper */
> >         std::unique_ptr<CameraSensorHelper> camHelper_;
> >  
> > @@ -195,8 +197,8 @@ void IPAIPU3::updateSessionConfiguration(const IPACameraSensorInfo &sensorInfo,
> >         int32_t minExposure = v4l2Exposure.min().get<int32_t>();
> >         int32_t maxExposure = v4l2Exposure.max().get<int32_t>();
> >  
> > -       utils::Duration lineDuration = sensorInfo.lineLength * 1.0s
> > -                                    / sensorInfo.pixelRate;
> > +       lineDuration_ = sensorInfo.lineLength * 1.0s
> > +                     / sensorInfo.pixelRate;
> >  
> >         const ControlInfo &v4l2Gain = sensorControls.find(V4L2_CID_ANALOGUE_GAIN)->second;
> >         int32_t minGain = v4l2Gain.min().get<int32_t>();
> > @@ -209,8 +211,8 @@ void IPAIPU3::updateSessionConfiguration(const IPACameraSensorInfo &sensorInfo,
> >          *
> >          * \todo take VBLANK into account for maximum shutter speed
> >          */
> > -       context_.configuration.agc.minShutterSpeed = minExposure * lineDuration;
> > -       context_.configuration.agc.maxShutterSpeed = maxExposure * lineDuration;
> > +       context_.configuration.agc.minShutterSpeed = minExposure * lineDuration_;
> > +       context_.configuration.agc.maxShutterSpeed = maxExposure * lineDuration_;
> >         context_.configuration.agc.minAnalogueGain = camHelper_->gain(minGain);
> >         context_.configuration.agc.maxAnalogueGain = camHelper_->gain(maxGain);
> >  }
> > @@ -239,11 +241,10 @@ void IPAIPU3::updateControls(const IPACameraSensorInfo &sensorInfo,
> >          * exposure min, max and default and convert it from lines to
> >          * microseconds.
> >          */
> > -       double lineDuration = sensorInfo.lineLength / (sensorInfo.pixelRate / 1e6);
> 
> I like that we get rid of this 1e6 though ;-)

It 'might' still be right - but needs a correct/thorough checking (or
use the explicit .get<std::nano>() / .get<std::micro>() ....

The 1e6 is I assume taking us to micro's?... but...

I believe the Duration.count() is going to be returning nano seconds...
can you validate/check that this calculation is using the correct units
as expected please?

I think this makes me favour the explicit units / period in the get<>()
call to make it clear what the calculation does..



> 
> >         const ControlInfo &v4l2Exposure = sensorControls.find(V4L2_CID_EXPOSURE)->second;
> > -       int32_t minExposure = v4l2Exposure.min().get<int32_t>() * lineDuration;
> > -       int32_t maxExposure = v4l2Exposure.max().get<int32_t>() * lineDuration;
> > -       int32_t defExposure = v4l2Exposure.def().get<int32_t>() * lineDuration;
> > +       int32_t minExposure = v4l2Exposure.min().get<int32_t>() * lineDuration_.count();
> > +       int32_t maxExposure = v4l2Exposure.max().get<int32_t>() * lineDuration_.count();
> > +       int32_t defExposure = v4l2Exposure.def().get<int32_t>() * lineDuration_.count();
> >         controls[&controls::ExposureTime] = ControlInfo(minExposure, maxExposure,
> >                                                         defExposure);
> >  
> > -- 
> > 2.32.0
> >