[PATCH] pipeline: simple: Increase buffer count to four

[Kieran Bingham]

Quoting Umang Jain (2024-09-27 08:09:48)
> Hi Robert,
> 
> Thank you for the patch.
> 
> On 27/09/24 2:37 am, Robert Mader wrote:
> > Which is not only what many other pipeline handlers use, but also a good
> > lower limit when dealing with DRM and similar APIs. Even Mesas EGL and
> > Vulkan WSI implementations use for the reason outlined in mesa commit
> > 992a2dbba80aba35efe83202e1013bd6143f0dba:
> >> When the compositor is directly scanning out from the application's buffer it
> >> may end up holding on to three buffers. These are the one that is is currently
> >> scanning out from, one that has been given to DRM as the next buffer to flip
> >> to, and one that has been attached and will be given to DRM as soon as the
> >> previous flip completes. When we attach a fourth buffer to the compositor it
> >> should replace that third buffer so we should get a release event immediately
> >> after that. This patch therefore also changes the number of buffer slots to 4
> >> so that we can accomodate that situation.
> > Given the popularity of this buffer number the bump should be unlikely
> > to cause problems. At the same time it may help with performance or
> > even work around glitches.
> >
> > The previous number was introduced in commit
> > a8964c28c80fb520ee3c7b10143371081d41405a without mentioning a specific
> > reason against the change at hand.
> >
> > Signed-off-by: Robert Mader <robert.mader at collabora.com>
> 
> Let's add to popularity then,
> 
> Reviewed-by: Umang Jain <umang.jain at ideasonboard.com>

This is fine for me too.


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

> > ---
> >   src/libcamera/pipeline/simple/simple.cpp | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/src/libcamera/pipeline/simple/simple.cpp b/src/libcamera/pipeline/simple/simple.cpp
> > index 81915573..78ce9232 100644
> > --- a/src/libcamera/pipeline/simple/simple.cpp
> > +++ b/src/libcamera/pipeline/simple/simple.cpp
> > @@ -1135,7 +1135,7 @@ CameraConfiguration::Status SimpleCameraConfiguration::validate()
> >                       cfg.frameSize = format.planes[0].size;
> >               }
> >   
> > -             cfg.bufferCount = 3;
> > +             cfg.bufferCount = 4;
> >       }
> >   
> >       return status;
>