[libcamera-devel] [PATCH v2 1/4] pipeline: rpi: Increase buffer import count to 32

[Kieran Bingham]

Quoting Jacopo Mondi via libcamera-devel (2023-07-27 10:31:28)
> Hi Naush
> 
> On Tue, Jul 25, 2023 at 09:55:37AM +0100, Naushir Patuck via libcamera-devel wrote:
> > Hardcode the maximum number of buffers imported to the V4L2 video device
> > to 32. This only has a minor disadvantage of over-allocating cache slots
> > and V4L2 buffer indexes, but does allow more headroom for using dma
> > buffers allocated from outside of libcamera.
> >
> > Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> > ---
> >  .../pipeline/rpi/common/rpi_stream.cpp        | 33 +++++--------------
> >  1 file changed, 8 insertions(+), 25 deletions(-)
> >
> > diff --git a/src/libcamera/pipeline/rpi/common/rpi_stream.cpp b/src/libcamera/pipeline/rpi/common/rpi_stream.cpp
> > index c158843cb0ed..e9ad1e6f0848 100644
> > --- a/src/libcamera/pipeline/rpi/common/rpi_stream.cpp
> > +++ b/src/libcamera/pipeline/rpi/common/rpi_stream.cpp
> > @@ -95,34 +95,17 @@ int Stream::prepareBuffers(unsigned int count)
> >       int ret;
> >
> >       if (!(flags_ & StreamFlag::ImportOnly)) {
> > -             if (count) {
> > -                     /* Export some frame buffers for internal use. */
> > -                     ret = dev_->exportBuffers(count, &internalBuffers_);
> > -                     if (ret < 0)
> > -                             return ret;
> > -
> > -                     /* Add these exported buffers to the internal/external buffer list. */
> > -                     setExportedBuffers(&internalBuffers_);
> > -                     resetBuffers();
> > -             }
> > +             /* Export some frame buffers for internal use. */
> > +             ret = dev_->exportBuffers(count, &internalBuffers_);
> > +             if (ret < 0)
> > +                     return ret;
> >
> > -             /* We must import all internal/external exported buffers. */
> > -             count = bufferMap_.size();
> > +             /* Add these exported buffers to the internal/external buffer list. */
> > +             setExportedBuffers(&internalBuffers_);
> > +             resetBuffers();
> >       }
> >
> > -     /*
> > -      * If this is an external stream, we must allocate slots for buffers that
> > -      * might be externally allocated. We have no indication of how many buffers
> > -      * may be used, so this might overallocate slots in the buffer cache.
> > -      * Similarly, if this stream is only importing buffers, we do the same.
> > -      *
> > -      * \todo Find a better heuristic, or, even better, an exact solution to
> > -      * this issue.
> > -      */
> > -     if ((flags_ & StreamFlag::External) || (flags_ & StreamFlag::ImportOnly))
> > -             count = count * 2;
> > -
> > -     return dev_->importBuffers(count);
> > +     return dev_->importBuffers(32);
> 
> Might be good to define 32 somewhere as constexpr to avoid magic
> numbers, but apart from this

Agreed here. Something like

/** The maximum buffer allocation possible with V4L2 */
constexpr maximumV4L2Buffers = 32;

to express that this is the maximum possible with V4L2....

But otherwise

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

> 
> Reviewed-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>
> 
> Thanks
>   j
> 
> >  }
> >
> >  int Stream::queueBuffer(FrameBuffer *buffer)
> > --
> > 2.34.1
> >