[libcamera-devel] [PATCH v2 15/17] android: capabilities: Cap frame rate to 30 FPS

[Laurent Pinchart]

Hello,

On Wed, Sep 08, 2021 at 09:36:20AM +0900, paul.elder at ideasonboard.com wrote:
> On Tue, Sep 07, 2021 at 09:41:05PM +0200, Jacopo Mondi wrote:
> > Limit the reported minumum frame duration to 30 FPS.
> > 
> > The reason to do is to bring the libcamra HAL in par with the Intel
> > HAL implementation on IPU3 platform, where 30FPS is the frame rate used
> > to perform quality tuning in the closed-source IPA module and has been
> > validated as the most efficient rate for the power/performace budget.
> > 
> > This change bring into the HAL a platform specific constraints, which
> > might be opportune for most platforms but should rather be configurable
> > by system integrators. Record that with a \todo entry.
> > 
> > Also record that, even if we report a lower frame rate, we currently
> > do not limit what the camera actually produce.
> 
> Hm, now I'm starting to wonder if we should cap the reported min frame
> duration in the HAL, but allow libcamera to go as fast as any user
> wants. But then we also need a way to actually set the frame duration in
> libcamera...
> 
> If the HAL reports max 30fps, then the HAL will only request up to
> 30fps, and then we can just set that on libcamera's side... that way we
> satisfy the HAL requirements while keeping the flexibility on
> libcamera's side.
> 
> Or would it be better to limit libcamera's IPU3 as well, since 30fps has
> been confirmed to be the best? "We know what the user wants more than
> the user knows what they want"

I'd rather go with this patch, I don't think libcamera should limit the
frame rate artifically on IPU3.

> > Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> > ---
> >  src/android/camera_capabilities.cpp | 23 +++++++++++++++++++++++
> >  1 file changed, 23 insertions(+)
> > 
> > diff --git a/src/android/camera_capabilities.cpp b/src/android/camera_capabilities.cpp
> > index deaec3282fd7..cff1e30a9567 100644
> > --- a/src/android/camera_capabilities.cpp
> > +++ b/src/android/camera_capabilities.cpp
> > @@ -632,6 +632,29 @@ int CameraCapabilities::initializeStreamConfigurations()
> >  
> >  			int64_t minFrameDuration = frameDurations->second.min().get<int64_t>() * 1000;
> >  			int64_t maxFrameDuration = frameDurations->second.max().get<int64_t>() * 1000;
> > +
> > +			/*
> > +			 * Cap min frame duration to 30 FPS.
> > +			 *
> > +			 * 30 frames per second has been validated as the most
> > +			 * opportune frame rate for quality tuning, and power
> > +			 * vs performances budget on Intel IPU3.

I'd say "on Intel IPU3-based Chromebooks", as this budget decision is
device-specific.

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> > +			 *
> > +			 * \todo This is a platform-specific decision that needs
> > +			 * to be abstracted and delegated to the configuration
> > +			 * file.
> > +			 *
> > +			 * \todo libcamera only allows to control frame duration
> > +			 * through the per-request controls::FrameDuration
> > +			 * control. If we cap the durations here, we should be
> > +			 * capable of configuring the camera to operate at such
> > +			 * duration without requiring to have the FrameDuration
> > +			 * control to be specified for each Request. Defer this
> > +			 * to the in-development configuration API rework.
> > +			 */
> > +			if (minFrameDuration < 1e9 / 30.0)
> > +				minFrameDuration = 1e9 / 30.0;
> > +
> >  			streamConfigurations_.push_back({
> >  				res, androidFormat, minFrameDuration, maxFrameDuration,
> >  			});

-- 
Regards,

Laurent Pinchart