[PATCH RFC v3 2/5] PCI: pciehp: Add pci_hp_wait_link_change()

[Abhin Parekadan Jose <abhinjoses@gmail.com>]

pci_hp_spurious_link_change() awaits the end of a code section causing
spurious link changes, such as a Secondary Bus Reset, and then tells
whether such a section has executed, using test_and_clear_bit() on
PCI_LINK_CHANGED. The answer is one-shot: only the first caller sees
true.

Split the wait out into pci_hp_wait_link_change(), which leaves
PCI_LINK_CHANGED alone, and implement pci_hp_spurious_link_change() on
top of it. Test PCI_LINK_CHANGING with test_bit_acquire(), so that the
caller's subsequent accesses are ordered after the end of the code
section even if wait_event() returns without sleeping. No functional
change intended.

Signed-off-by: Abhin Parekadan Jose <abhinjoses@gmail.com>
Assisted-by: LLM

---
Changes since RFC v2:
- Test PCI_LINK_CHANGING with test_bit_acquire(). (Sashiko)

RFC v2: https://lore.kernel.org/all/20260927165459.829900-3-abhinjoses@gmail.com/
Sashiko review of v2: https://lore.kernel.org/all/20260927170355.759301F000FF@smtp.kernel.org/
---
 drivers/pci/hotplug/pci_hotplug_core.c | 21 +++++++++++++++++++--
 drivers/pci/pci.h                      |  1 +
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/hotplug/pci_hotplug_core.c b/drivers/pci/hotplug/pci_hotplug_core.c
index fadcf98a8a660..75524fe2bec6e 100644
--- a/drivers/pci/hotplug/pci_hotplug_core.c
+++ b/drivers/pci/hotplug/pci_hotplug_core.c
@@ -528,6 +528,24 @@ void pci_hp_unignore_link_change(struct pci_dev *pdev)
 	wake_up_all(&pci_hp_link_change_wq);
 }
 
+/**
+ * pci_hp_wait_link_change - await end of code section causing spurious link changes
+ * @pdev: PCI hotplug bridge
+ *
+ * Await the end of a concurrently executing code section which is causing
+ * spurious link changes on the Secondary Bus of @pdev, if there is one.
+ *
+ * Unlike pci_hp_spurious_link_change(), leave the record that such a code
+ * section has executed in place.  May be called by hotplug drivers which need
+ * the link to have settled, but not the cause of a link change, so that they
+ * don't take the answer away from the caller of pci_hp_spurious_link_change().
+ */
+void pci_hp_wait_link_change(struct pci_dev *pdev)
+{
+	wait_event(pci_hp_link_change_wq,
+		   !test_bit_acquire(PCI_LINK_CHANGING, &pdev->priv_flags));
+}
+
 /**
  * pci_hp_spurious_link_change - check for spurious link changes
  * @pdev: PCI hotplug bridge
@@ -551,8 +569,7 @@ void pci_hp_unignore_link_change(struct pci_dev *pdev)
  */
 bool pci_hp_spurious_link_change(struct pci_dev *pdev)
 {
-	wait_event(pci_hp_link_change_wq,
-		   !test_bit(PCI_LINK_CHANGING, &pdev->priv_flags));
+	pci_hp_wait_link_change(pdev);
 
 	return test_and_clear_bit(PCI_LINK_CHANGED, &pdev->priv_flags);
 }
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 175273756c183..cfa0202bf610b 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -360,6 +360,7 @@ static inline int pci_proc_detach_bus(struct pci_bus *bus) { return 0; }
 
 /* Functions for PCI Hotplug drivers to use */
 int pci_hp_add_bridge(struct pci_dev *dev);
+void pci_hp_wait_link_change(struct pci_dev *pdev);
 bool pci_hp_spurious_link_change(struct pci_dev *pdev);
 
 /* Lock for read/write access to pci device and bus lists */
-- 
2.51.1