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Subject[PATCH 9/9] media: staging/imx: update TODO
Date
Update TODO file:

- Remove TODO info about the OV564x driver, while this still needs
to be done (add a OV5642 driver or merge with OV5640 driver), it
is not relevant here.

- Update TODO about methods for retrieving CSI bus config.

- Add some TODO's about OF graph parsing restrictions.

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
---
drivers/staging/media/imx/TODO | 63 ++++++++++++++++++++++++++++++++++--------
1 file changed, 51 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/media/imx/TODO b/drivers/staging/media/imx/TODO
index 0bee313..9eb7326 100644
--- a/drivers/staging/media/imx/TODO
+++ b/drivers/staging/media/imx/TODO
@@ -1,19 +1,14 @@

-- Clean up and move the ov5642 subdev driver to drivers/media/i2c, or
- merge support for OV5642 into drivers/media/i2c/ov5640.c, and create
- the binding docs for it.
-
- The Frame Interval Monitor could be exported to v4l2-core for
general use.

-- At driver load time, the device-tree node that is the original source
- (the "sensor"), is parsed to record its media bus configuration, and
- this info is required in imx-media-csi.c 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 mbus config
- method until this issue is resolved.
+- 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
@@ -21,3 +16,47 @@
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.
--
2.7.4
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