On Mon, May 08, 2023 at 08:41:42PM +0300, Sakari Ailus wrote: > On Mon, May 08, 2023 at 07:35:04PM +0300, Tomi Valkeinen wrote: > > On 08/05/2023 19:26, Sakari Ailus wrote: > > > On Mon, May 08, 2023 at 01:33:24PM +0300, Tomi Valkeinen wrote: > > > > On 06/05/2023 00:52, Sakari Ailus wrote: > > > > > Document how internal pads are used on source routes. > > > > > > > > > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> > > > > > --- > > > > > .../userspace-api/media/v4l/dev-subdev.rst | 18 ++++++++++++++++++ > > > > > .../media/v4l/vidioc-subdev-g-routing.rst | 5 +++++ > > > > > include/uapi/linux/v4l2-subdev.h | 6 +++++- > > > > > 3 files changed, 28 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst > > > > > index a4f1df7093e8..395e06d2f0f2 100644 > > > > > --- a/Documentation/userspace-api/media/v4l/dev-subdev.rst > > > > > +++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst > > > > > @@ -551,6 +551,24 @@ A stream at a specific point in the media pipeline is identified by the > > > > > sub-device and a (pad, stream) pair. For sub-devices that do not support > > > > > multiplexed streams the 'stream' field is always 0. > > > > > +.. _v4l2-subdev-source-routes: > > > > > + > > > > > +Source routes > > > > > +^^^^^^^^^^^^^ > > > > > + > > > > > +Cases where a single sub-device pad is a source of multiple streams are special > > > > > +as there is no sink pad for such a route. In those cases, an internal pad is > > > > > +used as the sink pad. Such pads have the :ref:`MEDIA_PAD_FL_INTERNAL_SOURCE > > > > > +<MEDIA-PAD-FL-INTERNAL-SOURCE>` flag set. > > > > > + > > > > > +Internal pads have all the properties of a sink pad in such case, including > > > > > +formats and selections. The format in this case is the source format of the > > > > > +stream. An internal pad always has a single stream only (0). > > > > > + > > > > > +Generally source routes are not modifiable but they can be activated and > > > > > +inactivated using the :ref:`V4L2_SUBDEV_ROUTE_FL_ACTIVE > > > > > +<v4l2-subdev-routing-flags>` flag, depending on driver capabilities. > > > > > + > > > > > > > > I find the above chapter a bit difficult to read, but I think we need to > > > > conclude on the internal-pad vs internal-source-pad discussion first. > > > > However, one point/question: > > > > > > > > You write that there's only one stream in an internal pad. I wonder if > > > > that's a good or a necessary limitation... Do you see that allowing multiple > > > > streams brings extra complexity? It's still up to each driver to decide how > > > > many streams they support (most would just support a single one), so each > > > > driver can easily enforce that limit. > > > > > > Good question. As we don't seem to have a tangible reason to allow it, I'd > > > deny it until there's a use case. > > > > > > Or did you have a use case in mind? > > > > > > I thought indicating which streams will be bound together (i.e. either are > > > all disabled or enabled) could be one, but I'm not sure we need that at the > > > moment at least. > > > > I don't have nothing concrete in mind. Maybe a TPG which also generates some > > kind of metadata. But that could be implemented as two internal pads. > > > > > > I'm fine with starting with only single-stream support, but if we later need > > > > to loosen that restriction, I wonder if it'll be difficult if we have > > > > specified that there can be only one stream. I.e. will the drivers and the > > > > userspace depend on that limit. > > > > > > We can always allow what wasn't allowed previously so that's a non-issue, > > > really. But it needs to bring new functionality, otherwise there's no > > > reason to do that. > > > > It's not always that easy. If the drivers and the userspace expect that > > there's a single route with ID 0, and then with a new kernel there are more > > streams or the single stream is ID 1, things could go wrong. > > Other drivers are a non-issue IMO as this isn't visible to other drivers. > > I think for user space this could be an issue if it were entirely generic. > But that's probably not going to be the case, is it? I don't mean test > programs. I could imagine this breaking libcamera for instance. -- Regards, Laurent Pinchart
