[PATCH RFC v3 3/5] PCI/DPC: Add pci_dpc_wait_recovery()

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

pci_dpc_recovered() awaits completion of DPC recovery and then tells
whether DPC recovered successfully, using test_and_clear_bit() on
PCI_DPC_RECOVERED. The answer is one-shot: only the first caller sees
true.

Split pci_dpc_recovered() into:

 - pci_dpc_hp_sync_supported(), the check whether hotplug can
   synchronize with DPC at all.
 - dpc_wait_completed(), the wait for recovery with its 4 second
   timeout;
 - the final test_and_clear_bit().

Add pci_dpc_wait_recovery(), which does the check and the wait but
leaves PCI_DPC_RECOVERED alone. No functional change intended.

Signed-off-by: Abhin Parekadan Jose <abhinjoses@gmail.com>
Assisted-by: LLM
---
 drivers/pci/pci.h      |  2 ++
 drivers/pci/pcie/dpc.c | 54 ++++++++++++++++++++++++++++++++----------
 2 files changed, 44 insertions(+), 12 deletions(-)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index cfa0202bf610b..b1d9df904c625 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -941,12 +941,14 @@ void pci_restore_dpc_state(struct pci_dev *dev);
 void pci_dpc_init(struct pci_dev *pdev);
 void dpc_process_error(struct pci_dev *pdev);
 pci_ers_result_t dpc_reset_link(struct pci_dev *pdev);
+void pci_dpc_wait_recovery(struct pci_dev *pdev);
 bool pci_dpc_recovered(struct pci_dev *pdev);
 unsigned int dpc_tlp_log_len(struct pci_dev *dev);
 #else
 static inline void pci_save_dpc_state(struct pci_dev *dev) { }
 static inline void pci_restore_dpc_state(struct pci_dev *dev) { }
 static inline void pci_dpc_init(struct pci_dev *pdev) { }
+static inline void pci_dpc_wait_recovery(struct pci_dev *pdev) { }
 static inline bool pci_dpc_recovered(struct pci_dev *pdev) { return false; }
 #endif
 
diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
index 2b779bd1d861b..a6438a7e3d9c7 100644
--- a/drivers/pci/pcie/dpc.c
+++ b/drivers/pci/pcie/dpc.c
@@ -92,15 +92,7 @@ static bool dpc_completed(struct pci_dev *pdev)
 	return true;
 }
 
-/**
- * pci_dpc_recovered - whether DPC triggered and has recovered successfully
- * @pdev: PCI device
- *
- * Return true if DPC was triggered for @pdev and has recovered successfully.
- * Wait for recovery if it hasn't completed yet.  Called from the PCIe hotplug
- * driver to recognize and ignore Link Down/Up events caused by DPC.
- */
-bool pci_dpc_recovered(struct pci_dev *pdev)
+static bool pci_dpc_hp_sync_supported(struct pci_dev *pdev)
 {
 	struct pci_host_bridge *host;
 
@@ -108,13 +100,18 @@ bool pci_dpc_recovered(struct pci_dev *pdev)
 		return false;
 
 	/*
-	 * Synchronization between hotplug and DPC is not supported
-	 * if DPC is owned by firmware and EDR is not enabled.
-	 */
+	* Synchronization between hotplug and DPC is only supported if DPC is owned
+	* by the OS, or by firmware with EDR enabled.
+	*/
 	host = pci_find_host_bridge(pdev->bus);
 	if (!host->native_dpc && !IS_ENABLED(CONFIG_PCIE_EDR))
 		return false;
 
+	return true;
+}
+
+static void dpc_wait_completed(struct pci_dev *pdev)
+{
 	/*
 	 * Need a timeout in case DPC never completes due to failure of
 	 * dpc_wait_rp_inactive().  The spec doesn't mandate a time limit,
@@ -122,6 +119,39 @@ bool pci_dpc_recovered(struct pci_dev *pdev)
 	 */
 	wait_event_timeout(dpc_completed_waitqueue, dpc_completed(pdev),
 			   msecs_to_jiffies(4000));
+}
+
+/**
+ * pci_dpc_wait_recovery - await completion of DPC recovery
+ * @pdev: PCI device
+ *
+ * Wait for recovery if DPC was triggered for @pdev and recovery hasn't
+ * completed yet.  Unlike pci_dpc_recovered(), leave the record of a
+ * successful recovery in place.  Called from the PCIe hotplug driver where
+ * it needs the link to have settled, but not the cause of a link change.
+ * Nothing is awaited if synchronization between hotplug and DPC is not
+ * supported for @pdev.
+ */
+void pci_dpc_wait_recovery(struct pci_dev *pdev)
+{
+	if (pci_dpc_hp_sync_supported(pdev))
+		dpc_wait_completed(pdev);
+}
+
+/**
+ * pci_dpc_recovered - whether DPC triggered and has recovered successfully
+ * @pdev: PCI device
+ *
+ * Return true if DPC was triggered for @pdev and has recovered successfully.
+ * Wait for recovery if it hasn't completed yet.  Called from the PCIe hotplug
+ * driver to recognize and ignore Link Down/Up events caused by DPC.
+ */
+bool pci_dpc_recovered(struct pci_dev *pdev)
+{
+	if (!pci_dpc_hp_sync_supported(pdev))
+		return false;
+
+	dpc_wait_completed(pdev);
 
 	return test_and_clear_bit(PCI_DPC_RECOVERED, &pdev->priv_flags);
 }
-- 
2.51.1