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

[Kieran Bingham]

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>

> 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 ;-)

>         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
>