linux-kernel - [PATCH] of: property: Create devlink between PCI Host bridge and Root Port suppliers

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Message-ID: <20260205070640.10653-1-manivannan.sadhasivam@oss.qualcomm.com>
Date: Thu,  5 Feb 2026 12:36:40 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
To: robh@...nel.org, saravanak@...nel.org
Cc: andersson@...nel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        qiang.yu@....qualcomm.com,
        Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
Subject: [PATCH] of: property: Create devlink between PCI Host bridge and Root Port suppliers

In the recent times, devicetree started to represent the PCI Host bridge
supplies like PHY in the Root Port nodes as seen in commit 38fcbfbd4207
("dt-bindings: PCI: qcom: Move PHY & reset GPIO to Root Port node"). But
the Host bridge drivers still need to control these supplies as a part of
their controller initialization/deinitialization sequence.

So the Host bridge drivers end up parsing the Root Port supplies in their
probe() and controlled them. A downside to this approach is that the
devlink dependency between the suppliers and Host bridge is completely
broken. Due to this, the driver core probes the Host bridge drivers even if
the suppliers are not ready, causing probe deferrals and setup teardowns in
probe().

These probe deferrals sometime happen over 1000 times (as reported in Qcom
Glymur platform) leading to a waste of CPU resources and increase in boot
time. So to fix these unnecessary deferrals, create devlink between the
Host bridge and Root Port suppliers in of_fwnode_add_links(). This will
allow the driver core to probe the Host bridge drivers only when all Root
Port suppliers are available.

Reported-by: Bjorn Andersson <andersson@...nel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
---
 drivers/of/property.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/of/property.c b/drivers/of/property.c
index 50d95d512bf5..10d041ea61f7 100644
--- a/drivers/of/property.c
+++ b/drivers/of/property.c
@@ -1561,6 +1561,7 @@ static const struct supplier_bindings of_supplier_bindings[] = {
 /**
  * of_link_property - Create device links to suppliers listed in a property
  * @con_np: The consumer device tree node which contains the property
+ * @parent_np: Optional parent device tree node requiring child's supplies
  * @prop_name: Name of property to be parsed
  *
  * This function checks if the property @prop_name that is present in the
@@ -1577,7 +1578,8 @@ static const struct supplier_bindings of_supplier_bindings[] = {
  * device tree nodes even when attempts to create a link to one or more
  * suppliers fail.
  */
-static int of_link_property(struct device_node *con_np, const char *prop_name)
+static int of_link_property(struct device_node *con_np, struct device_node *parent_np,
+			    const char *prop_name)
 {
 	struct device_node *phandle;
 	const struct supplier_bindings *s = of_supplier_bindings;
@@ -1598,6 +1600,10 @@ static int of_link_property(struct device_node *con_np, const char *prop_name)
 			matched = true;
 			i++;
 			of_link_to_phandle(con_dev_np, phandle, s->fwlink_flags);
+
+			/* Link the child's supplies to parent if needed */
+			if (parent_np)
+				of_link_to_phandle(parent_np, phandle, s->fwlink_flags);
 			of_node_put(phandle);
 		}
 		s++;
@@ -1632,7 +1638,21 @@ static int of_fwnode_add_links(struct fwnode_handle *fwnode)
 		return -EINVAL;
 
 	for_each_property_of_node(con_np, p)
-		of_link_property(con_np, p->name);
+		of_link_property(con_np, NULL, p->name);
+
+	/*
+	 * Supplies for the PCI host bridges are typically present in the Root
+	 * Port nodes. So parse the Root Port supplies and link them to Host
+	 * bridges (identified by the presence of "linux,pci-domain" property).
+	 */
+	if (of_property_present(con_np, "linux,pci-domain")) {
+		for_each_available_child_of_node_scoped(con_np, child) {
+			if (of_node_is_type(child, "pci")) {
+				for_each_property_of_node(child, p)
+					of_link_property(child, con_np, p->name);
+			}
+		}
+	}
 
 	return 0;
 }
-- 
2.51.0