driver core: fw_devlink: Improve detection of overlapping cycles

driver core: fw_devlink: Improve detection of overlapping cycles

[ Upstream commit 6442d79d880cf7a2fff18779265d657fef0cce4c ]

fw_devlink can detect most overlapping/intersecting cycles. However it was
missing a few corner cases because of an incorrect optimization logic that
tries to avoid repeating cycle detection for devices that are already
marked as part of a cycle.

Here's an example provided by Xu Yang (edited for clarity):

                    usb
                  +-----+
   tcpc           |     |
  +-----+         |  +--|
  |     |----------->|EP|
  |--+  |         |  +--|
  |EP|<-----------|     |
  |--+  |         |  B  |
  |     |         +-----+
  |  A  |            |
  +-----+            |
     ^     +-----+   |
     |     |     |   |
     +-----|  C  |<--+
           |     |
           +-----+
           usb-phy

Node A (tcpc) will be populated as device 1-0050.
Node B (usb) will be populated as device 38100000.usb.
Node C (usb-phy) will be populated as device 381f0040.usb-phy.

The description below uses the notation:
consumer --> supplier
child ==> parent

1. Node C is populated as device C. No cycles detected because cycle
   detection is only run when a fwnode link is converted to a device link.

2. Node B is populated as device B. As we convert B --> C into a device
   link we run cycle detection and find and mark the device link/fwnode
   link cycle:
   C--> A --> B.EP ==> B --> C

3. Node A is populated as device A. As we convert C --> A into a device
   link, we see it's already part of a cycle (from step 2) and don't run
   cycle detection. Thus we miss detecting the cycle:
   A --> B.EP ==> B --> A.EP ==> A

Looking at it another way, A depends on B in one way:
A --> B.EP ==> B

But B depends on A in two ways and we only detect the first:
B --> C --> A
B --> A.EP ==> A

To detect both of these, we remove the incorrect optimization attempt in
step 3 and run cycle detection even if the fwnode link from which the
device link is being created has already been marked as part of a cycle.

Reported-by: Xu Yang <xu.yang_2@nxp.com>
Closes: https://lore.kernel.org/lkml/DU2PR04MB8822693748725F85DC0CB86C8C792@DU2PR04MB8822.eurprd04.prod.outlook.com/
Fixes: 3fb16866b51d ("driver core: fw_devlink: Make cycle detection more robust")
Signed-off-by: Saravana Kannan <saravanak@google.com>
Tested-by: Xu Yang <xu.yang_2@nxp.com>
Link: https://lore.kernel.org/r/20240202095636.868578-3-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>