[RFC PATCH 3/8] PCI/PM: Convert pci_bridge_d3_update() recursion to iteration

[Pavol Sakac <sakacpav@amazon.de>]

pci_bridge_d3_update() propagates a bridge_d3 change to upstream bridges
by tail recursion: when a bridge's bridge_d3 value changes, the function
calls itself with that bridge as the new device.

Convert the tail recursion into an iterative loop. Each level recomputes
"remove" and d3cold_ok exactly as the recursive call did for its own
device, and the early returns become loop exits. No functional change
intended.

An upcoming change serializes this update with a mutex; the iterative
form lets that mutex be taken once per external call instead of once per
bridge level.

Assisted-by: LLM
Signed-off-by: Pavol Sakac <sakacpav@amazon.de>
---
 drivers/pci/pci.c | 67 +++++++++++++++++++++++++----------------------
 1 file changed, 35 insertions(+), 32 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b2879a6be5f8..c62a315c0b4c 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3104,46 +3104,49 @@ static int pci_dev_check_d3cold(struct pci_dev *dev, void *data)
  */
 void pci_bridge_d3_update(struct pci_dev *dev)
 {
-	bool remove = !device_is_registered(&dev->dev);
 	struct pci_dev *bridge;
-	bool d3cold_ok = true;
 
-	bridge = pci_upstream_bridge(dev);
-	if (!bridge || !pci_bridge_d3_possible(bridge))
-		return;
+	while ((bridge = pci_upstream_bridge(dev)) &&
+	       pci_bridge_d3_possible(bridge)) {
+		bool remove = !device_is_registered(&dev->dev);
+		bool d3cold_ok = true;
 
-	/*
-	 * If D3 is currently allowed for the bridge, removing one of its
-	 * children won't change that.
-	 */
-	if (remove && bridge->bridge_d3)
-		return;
+		/*
+		 * If D3 is currently allowed for the bridge, removing one of
+		 * its children won't change that.
+		 */
+		if (remove && bridge->bridge_d3)
+			break;
 
-	/*
-	 * If D3 is currently allowed for the bridge and a child is added or
-	 * changed, disallowance of D3 can only be caused by that child, so
-	 * we only need to check that single device, not any of its siblings.
-	 *
-	 * If D3 is currently not allowed for the bridge, checking the device
-	 * first may allow us to skip checking its siblings.
-	 */
-	if (!remove)
-		pci_dev_check_d3cold(dev, &d3cold_ok);
+		/*
+		 * If D3 is currently allowed for the bridge and a child is
+		 * added or changed, disallowance of D3 can only be caused by
+		 * that child, so we only need to check that single device,
+		 * not any of its siblings.
+		 *
+		 * If D3 is currently not allowed for the bridge, checking the
+		 * device first may allow us to skip checking its siblings.
+		 */
+		if (!remove)
+			pci_dev_check_d3cold(dev, &d3cold_ok);
 
-	/*
-	 * If D3 is currently not allowed for the bridge, this may be caused
-	 * either by the device being changed/removed or any of its siblings,
-	 * so we need to go through all children to find out if one of them
-	 * continues to block D3.
-	 */
-	if (d3cold_ok && !bridge->bridge_d3)
-		pci_walk_bus(bridge->subordinate, pci_dev_check_d3cold,
-			     &d3cold_ok);
+		/*
+		 * If D3 is currently not allowed for the bridge, this may be
+		 * caused either by the device being changed/removed or any of
+		 * its siblings, so we need to go through all children to find
+		 * out if one of them continues to block D3.
+		 */
+		if (d3cold_ok && !bridge->bridge_d3)
+			pci_walk_bus(bridge->subordinate, pci_dev_check_d3cold,
+				     &d3cold_ok);
+
+		if (bridge->bridge_d3 == d3cold_ok)
+			break;
 
-	if (bridge->bridge_d3 != d3cold_ok) {
 		bridge->bridge_d3 = d3cold_ok;
+
 		/* Propagate change to upstream bridges */
-		pci_bridge_d3_update(bridge);
+		dev = bridge;
 	}
 }
 
-- 
2.47.3