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.
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.
Tomi
