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

[Kieran Bingham]

Quoting Naushir Patuck (2023-01-20 11:34:30)
> On Fri, 20 Jan 2023 at 11:27, Kieran Bingham <
> kieran.bingham at ideasonboard.com> wrote:
> 
> > 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?
> >
> 
> In earlier versions of this series, these hints were effectively flags in
> the config files.
> It was suggested to move these into the StreamConfig as hints since they
> may be useful to other pipeline handlers, and enforce explicit application
> behavior through the API.
> 

Ok - in that case, that confirms that the checks/assertions in [9/12]
should be in the core, not just against raspberry pi pipeline handler.

This may also require updating any tests that could be affected, and
lc-compliance.

It may be helpful to split out this core API 'hint's part to it's own
series as I don't think it should necessarily block the configuration
file work here.

--
KB


> > > 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
> >