of: property: Improve cycle detection when one of the devices is never added

Consider this example where -> means LHS device is a consumer of RHS
device and indentation represents "child of" of the previous device.

Device A -> Device C

Device B -> Device A
	Device C

Without this commit:
1. Device A is added.
2. Device A is added to waiting for supplier list (Device C)
3. Device B is added
4. Device B is linked as a consumer to Device A
5. Device A doesn't probe because it's waiting for Device C to be added.
6. Device B doesn't probe because Device A hasn't probed.
7. Device C will never be added because it's parent hasn't probed.

So, Device A, B and C will be in a probe/add deadlock.

This commit detects this scenario and stops trying to create a device
link between Device A and Device C since doing so would create the
following cycle:
Device A -> Devic C -(parent)-> Device B -> Device A.

With this commit:
1. Device A is added.
3. Device B is added
4. Device B is linked as a consumer to Device A
5. Device A probes.
6. Device B probes because Device A has probed.
7. Device C is added and probed.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20200610011934.49795-3-saravanak@google.com
Signed-off-by: Rob Herring <robh@kernel.org>

0 files changed, 0 insertions, 0 deletions