[libcamera-devel] [PATCH 02/13] libcamera: ipu3: Import instead of allocate statistic buffers

[Niklas Söderlund]

Hi Jacopo,

Thanks for your feedback.

On 2020-06-27 11:51:32 +0200, Jacopo Mondi wrote:
> Hi Niklas,
> 
> On Sat, Jun 27, 2020 at 05:00:32AM +0200, Niklas Söderlund wrote:
> > Statistics buffers are not yet used by the IPU3 pipeline, they are never
> > queued to the video device or in any other way consumed. The kernel
> > driver will however not allow video streaming to start if buffers are
> > not either allocated or imported on the video device. Instead of
> > allocating the buffers wasting memory that is never used import buffers.
> >
> > Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> > ---
> >  src/libcamera/pipeline/ipu3/ipu3.cpp | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/src/libcamera/pipeline/ipu3/ipu3.cpp b/src/libcamera/pipeline/ipu3/ipu3.cpp
> > index fba45935741e0e4e..405550b1302fb370 100644
> > --- a/src/libcamera/pipeline/ipu3/ipu3.cpp
> > +++ b/src/libcamera/pipeline/ipu3/ipu3.cpp
> > @@ -1135,11 +1135,13 @@ int ImgUDevice::allocateBuffers(IPU3CameraData *data, unsigned int bufferCount)
> >  	}
> >
> >  	/*
> > -	 * Use for the stat's internal pool the same number of buffers as for
> > -	 * the input pool.
> > +	 * The kernel fails to start if buffers are not either imported or
> > +	 * allocated for the statisitcs video device. As statistics buffers are
> > +	 * not yet used by the pipeline import buffers to save memory.
> > +	 *
> 
> Is this based on practical experience ? The IPU3 driver documentation
> is a bit confusing on which output is required to have buffes queued
> in order for operations to start...

Yes the documentation is not very helpful so this is all based on 
experimentation and reading the code. See the cover letter for how I 
verified it.

> 
> 
> >  	 * \todo To be revised when we'll actually use the stat node.
> >  	 */
> > -	ret = stat_.dev->allocateBuffers(bufferCount, &stat_.buffers);
> > +	ret = stat_.dev->importBuffers(bufferCount);
> >  	if (ret < 0) {
> >  		LOG(IPU3, Error) << "Failed to allocate ImgU stat buffers";
> >  		goto error;
> > --
> > 2.27.0
> >
> > _______________________________________________
> > libcamera-devel mailing list
> > libcamera-devel at lists.libcamera.org
> > https://lists.libcamera.org/listinfo/libcamera-devel

-- 
Regards,
Niklas Söderlund