[libcamera-devel] [PATCH v5 01/12] libcamera: stream: Add stream hints to StreamConfiguration

[Kieran Bingham]

Quoting Naushir Patuck (2023-01-20 10:53:38)
> On Fri, 20 Jan 2023 at 10:42, Kieran Bingham <
> kieran.bingham at ideasonboard.com> wrote:
> 
> > Quoting Naushir Patuck (2023-01-18 11:16:40)
> > > On Wed, 18 Jan 2023 at 10:09, Kieran Bingham <
> > > kieran.bingham at ideasonboard.com> wrote:
> > >
> > > > Hi Naush,
> > > >
> > > > Quoting Naushir Patuck via libcamera-devel (2023-01-18 08:59:42)
> > > > > Add a new hints flags field in the StreamConfiguration structure to
> > > > allow the
> > > > > application to specify certain intended behavior when driving
> > libcamera.
> > > > > Pipeline handlers are expected to look at these hint flags and may
> > > > optimise
> > > > > internal operations based on them.
> > > > >
> > > > > Currently, only one flag is listed, OptionalStream, which the
> > > > application can
> > > > > set to inform the pipeline handler that a buffer may not be provided
> > on
> > > > every
> > > > > Request for a given stream.
> > > >
> > > > Sorry - Laurent had comments on this yesterday when I was discussing
> > > > with him, so I don't know which way it will go yet...
> > > >
> > > > I still think this is the better way around, but we'll have to consider
> > > > that this is an 'ABI' breakage, as now apps that were able to use two
> > > > streams won't unless they explicitly provide all buffers or inform
> > > > libcamera that they won't provide all buffers....
> > > >
> > >
> > > In the earlier versions of this series, we didn't have hints but used
> > config
> > > params to indicate this.  Perhaps I should go back to this mechanism for
> > the
> > > time being to avoid any ABI breakages until there is an agreed path
> > forward?
> >
> > That's just swapping one ABI breakage for another - because then the
> > hint would change (or we'd have both a 'MandatoryStream' hint, and an
> > 'OptionalStream' hint ?)
> >
> 
> If the "hint" were to move back to the config file, I would make it such

Move back to ? Was there previous discussion that moved this out of a
config file that I've missed?


> that the value is true for applications that provide buffers for every
> configured stream on every request.
> This would be defaulted to false, and libcamera-apps/picamera2 would set a
> config file with the flag to true.  This would preserve behavior for any
> other existing applications that don't pass in a configuration file, though
> it may be suboptimal with allocations.  No ABI breakages either...

--
Kieran