linux-kernel - [PATCH] driver core: improve cycle detection on fwnode graph

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Date: Wed, 24 Jan 2024 16:46:36 +0800
From: Xu Yang <xu.yang_2@....com>
To: gregkh@...uxfoundation.org,
	rafael@...nel.org,
	saravanak@...gle.com
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] driver core: improve cycle detection on fwnode graph

Currently, cycle detection on fwnode graph is still defective.
Such as fwnode link A.EP->B is not marked as cycle in below case:

                 +-----+
                 |     |
 +-----+         |  +--|
 |     |<-----------|EP|
 |--+  |         |  +--|
 |EP|----------->|     |
 |--+  |         |  B  |
 |     |         +-----+
 |  A  |            ^
 +-----+   +-----+  |
    |      |     |  |
    +----->|  C  |--+
           |     |
           +-----+

1. Node C is populated as device C. But nodes A and B are still not
   populated. When do cycle detection with device C, no cycle is found.
2. Node B is populated as device B. When do cycle detection with device
   B, it found a link cycle B.EP->A->C->B. Then, fwnode link B.EP->A,
   A->C and C->B are marked as cycle. The fwnode link C->B is converted
   to device link too.
3. Node A is populated as device A. When do cycle detection with device
   A, it find A->C is marked as cycle and convert it to device link. It
   also find B.EP->A is marked as cycle but will not convert it to device
   link since node B.EP is not a device.

Finally, fwnode link C->B and A->C is removed, B.EP->A is only marked as
cycle and A.EP->B is neither been marked as cycle nor removed.

For fwnode graph, the endpoint node can only be a supplier of other node
and the endpoint node will never be populated as device. Therefore, when
creating device link to supplier for fwnode graph, we need to relax cycle
with the real node rather endpoint node.

Signed-off-by: Xu Yang <xu.yang_2@....com>
---
 drivers/base/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 14d46af40f9a..278ded6cd3ce 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2217,6 +2217,9 @@ static void __fw_devlink_link_to_suppliers(struct device *dev,
 		int ret;
 		struct fwnode_handle *sup = link->supplier;

+		if (fwnode_graph_is_endpoint(sup))
+			sup = fwnode_graph_get_port_parent(sup);
+
 		ret = fw_devlink_create_devlink(dev, sup, link);
 		if (!own_link || ret == -EAGAIN)
 			continue;
-- 
2.34.1