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media: staging/imx: TODO: Remove one assumption about OF graph parsing 

The move to subdev notifiers fixes one assumption of OF graph parsing.
If a subdevice has non-video related ports, the subdev driver knows not
to follow those ports when adding remote devices to its subdev notifier.

Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
This commit is contained in:
Steve Longerbeam 2018-09-29 15:54:17 -04:00 committed by Mauro Carvalho Chehab
parent b803cd3598
commit d5099f8180
1 changed files with 7 additions and 22 deletions
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29
drivers/staging/media/imx/TODO
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@ -17,29 +17,15 @@
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.
- After all async subdevices have been bound, v4l2_fwnode_parse_link()
is used to form the media links between the devices discovered in
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.
1. If a port owned by a device in the graph has endpoint nodes, the
port is treated as a media pad.
This presents problems for devices that don't make this port = pad
assumption. Examples are SMIAPP compatible cameras which define only
@ -54,9 +40,8 @@
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.
2. Every endpoint of a port owned by a device in the graph is treated
as a media link.
Which means a port must not contain mixed-use endpoints, they
must all refer to media links between V4L2 subdevices.