|
- The Frame Interval Monitor could be exported to v4l2-core for
|
general use.
|
|
- The CSI subdevice parses its nearest upstream neighbor's device-tree
|
bus config in order to setup the CSI. Laurent Pinchart argues that
|
instead the CSI subdev should call its neighbor's g_mbus_config op
|
(which should be propagated if necessary) to get this info. However
|
Hans Verkuil is planning to remove the g_mbus_config op. For now this
|
driver uses the parsed DT bus config method until this issue is
|
resolved.
|
|
- This media driver supports inheriting V4L2 controls to the
|
video capture devices, from the subdevices in the capture device's
|
pipeline. The controls for each capture device are updated in the
|
link_notify callback when the pipeline is modified. It should be
|
decided whether this feature is useful enough to make it generally
|
available by exporting to v4l2-core.
|
|
- The OF graph is walked at probe time to form the list of fwnodes to
|
be passed to v4l2_async_notifier_register(), starting from the IPU
|
CSI ports. And after all async subdevices have been bound,
|
v4l2_fwnode_parse_link() is used to form the media links between
|
the entities discovered by walking the OF graph.
|
|
While this approach allows support for arbitrary OF graphs, there
|
are some assumptions for this to work:
|
|
1. All port parent nodes reachable in the graph from the IPU CSI
|
ports bind to V4L2 async subdevice drivers.
|
|
If a device has mixed-use ports such as video plus audio, the
|
endpoints from the audio ports are followed to devices that must
|
bind to V4L2 subdevice drivers, and not for example, to an ALSA
|
driver or a non-V4L2 media driver. If the device were bound to
|
such a driver, imx-media would never get an async completion
|
notification because the device fwnode was added to the async
|
list, but the driver does not interface with the V4L2 async
|
framework.
|
|
2. Every port reachable in the graph is treated as a media pad,
|
owned by the V4L2 subdevice that is bound to the port's parent.
|
|
This presents problems for devices that don't make this port = pad
|
assumption. Examples are SMIAPP compatible cameras which define only
|
a single output port node, but which define multiple pads owned
|
by multiple subdevices (pixel-array, binner, scaler). Or video
|
decoders (entity function MEDIA_ENT_F_ATV_DECODER), which also define
|
only a single output port node, but define multiple pads for video,
|
VBI, and audio out.
|
|
A workaround at present is to set the port reg properties to
|
correspond to the media pad index that the port represents. A
|
possible long-term solution is to implement a subdev API that
|
maps a port id to a media pad index.
|
|
3. Every endpoint of a port reachable in the graph is treated as
|
a media link, between V4L2 subdevices that are bound to the
|
port parents of the local and remote endpoints.
|
|
Which means a port must not contain mixed-use endpoints, they
|
must all refer to media links between V4L2 subdevices.
|
