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

[Naushir Patuck]

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.


>
> > 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
>
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