On 03/10/2023 15:07, Sakari Ailus wrote:
Document S_ROUTING behaviour for different devices.
Generally in devices that produce streams the streams are static and some
I'm not sure what "static" means here. "Generally in devices that
produce streams there is a fixed amount of streams..."?
can be enabled and disabled, whereas in devices that just transport them
or write them to memory, more configurability is allowed. Document this.
Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
---
.../userspace-api/media/v4l/dev-subdev.rst | 21 +++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst
index fb73a95401c3..83993775237f 100644
--- a/Documentation/userspace-api/media/v4l/dev-subdev.rst
+++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst
@@ -593,6 +593,27 @@ Any configurations of a stream within a pad, such as format or selections,
are independent of similar configurations on other streams. This is
subject to change in the future.
+Device types and routing setup
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Different kinds of sub-devices have differing behaviour for route inactivation,
Would "activation" convey the same, but be a bit clearer?
+depending on the hardware. Devices generating the streams may often allow
Maybe drop the "often".
+enabling and disabling some of these or the configuration is fixed. If these
"some of these" -> "some of the routes".
+routes can be disabled, not declaring these routes (or declaring them without
Here also, I think "the routes" is more readable than repeating "these
routes".
+``VIDIOC_SUBDEV_STREAM_FL_ACTIVE`` flag set) in ``VIDIOC_SUBDEV_S_ROUTING`` will
Why is the flag sentence in parenthesis? Aren't both options of the same
value?
+disable the routes while the sub-device driver retain the streams and their
What does this mean? That even if the user disables a route, the driver
must keep the configuration that was set earlier related to that route?
+configuration. The ``VIDIOC_SUBDEV_S_ROUTING`` will still return such routes
+back to the user in the routes array, with the ``V4L2_SUBDEV_STREAM_FL_ACTIVE``
+flag unset.
So a generating device should always return all its routes with both
G_ROUTING and S_ROUTING, right? But with disabled routes not having
VIDIOC_SUBDEV_STREAM_FL_ACTIVE. The text doesn't mention G_ROUTING at all.
+Devices transporting the streams almost always have more configurability with
+respect to routing. Typically any route between the sub-device's sink and source
+pads is possible, and multiple routes (usually up to certain limited number) may
+be active simultaneously. For such devices, no routes are created by the driver
+and user-created routes are fully replaced when ``VIDIOC_SUBDEV_S_ROUTING`` is
+called on the sub-device. Such newly created routes have the device's default
+configuration for format and selection rectangles.
+
I think this paragraph is ok. But could this whole section be
restructured a bit, as the previous paragraph gets quite confusing. Maybe:
First paragraph to explain the two different kinds of devices, and
perhaps a mention that a route is considered disabled if either it does
not exist in the routing table or if VIDIOC_SUBDEV_STREAM_FL_ACTIVE is
not set.
Then a paragraph for generating devices, and then a paragraph for
transporting devices.
Configuring streams
^^^^^^^^^^^^^^^^^^^
