Re: [PATCH v5 00/17] media: imx: Switch to subdev notifiers

From: Steve Longerbeam
Date: Sat Jul 07 2018 - 17:15:36 EST

Hi Sakari,

On 07/02/2018 02:51 AM, Sakari Ailus wrote:
Hi Steve,

On Fri, Jun 29, 2018 at 11:49:44AM -0700, Steve Longerbeam wrote:
This patchset converts the imx-media driver and its dependent
subdevs to use subdev notifiers.

There are a couple shortcomings in v4l2-core that prevented
subdev notifiers from working correctly in imx-media:

1. v4l2_async_notifier_fwnode_parse_endpoint() treats a fwnode
endpoint that is not connected to a remote device as an error.
But in the case of the video-mux subdev, this is not an error,
it is OK if some of the mux inputs have no connection. Also,
Documentation/devicetree/bindings/media/video-interfaces.txt explicitly
states that the 'remote-endpoint' property is optional. So the first
patch is a small modification to ignore empty endpoints in
v4l2_async_notifier_fwnode_parse_endpoint() and allow
__v4l2_async_notifier_parse_fwnode_endpoints() to continue to
parse the remaining port endpoints of the device.

2. In the imx-media graph, multiple subdevs will encounter the same
upstream subdev (such as the imx6-mipi-csi2 receiver), and so
v4l2_async_notifier_parse_fwnode_endpoints() will add imx6-mipi-csi2
multiple times. This is treated as an error by
v4l2_async_notifier_register() later.

To get around this problem, add an v4l2_async_notifier_add_subdev()
which first verifies the provided asd does not already exist in the
given notifier asd list or in other registered notifiers. If the asd
exists, the function returns -EEXIST and it's up to the caller to
decide if that is an error (in imx-media case it is never an error).

Patches 2-5 deal with adding that support.

3. Patch 6 adds v4l2_async_register_fwnode_subdev(), which is a
convenience function for parsing a subdev's fwnode port endpoints
for connected remote subdevs, registering a subdev notifier, and
then registering the sub-device itself.

4. Patches 7-14 update the subdev drivers to register a subdev notifier
with endpoint parsing, and the changes to imx-media to support that.

5. Finally, the last 3 patches endeavor to completely remove support for
the notifier->subdevs[] array in platform drivers and v4l2 core. All
platform drivers are modified to make use of
v4l2_async_notifier_add_subdev() and its related convenience functions
to add asd's to the notifier @asd_list, and any allocation or reference
to the notifier->subdevs[] array removed. After that large patch,
notifier->subdevs[] array is stripped from v4l2-async and v4l2-subdev
docs are updated to reflect the new method of adding asd's to notifiers.

Thanks for the update! This is beginning to look really nice. A few notes
on the entire set. I'll separately review some of the patches; I mainly
wanted to see how the async/fwnode framework changes end up:

- The reason V4L2_MAX_SUBDEVS exists is to avoid drivers accidentally
allocating more space than intended. Now that the subdevs array will
disappear, the checks as well as the macro can be removed. I think the
num_subdevs field also becomes redundant as a result. Could you do this
in the patch that removes the subdevs array?

Yes, good idea, done! It was easy to do.

- The notifier has register, unregister and cleanup operations. Now that
there's an obvious need to initialise it, it'd make sense to show that to
the drivers as an init operation --- rather than silently initialise it
based on the need.

That was actually my plan initially, but at the time, it meant modifying
all platform drivers to call v4l2_async_notifier_init(). But since this patchset
now touches all platform drivers anyway, might as well do it.

Of course doing this adds more risk, since I have to call v4l2_async_notifier_init()
in the correct places. But cross-my-fingers, I think I've done this correctly.

- I'd assign j in its declaration in


- No need to explicitly check that the notifier's asd_list is empty in
__v4l2_async_notifier_register --- list_for_each_entry() over the same
list will be nop in that case.


I'm submitting v8 shortly.